linux.git/kernel/trace/trace_events_hist.c, branch v7.3-rc2 Linux kernel source tree tracing: Fix use-after-free with same-name named triggers 2026-08-22T21:33:57+00:00 Hui Su sh_def@163.com 2026-08-16T10:04:29+00:00 a7318172aa332a161fb9618286e64454c827f8fd When two hist triggers on different events are registered with the same name=, the second one reuses the first as named_data. Both are added to tr->hist_vars by save_hist_vars() during event_hist_trigger_parse(), because save_hist_vars() is called before event_trigger_register() while the named reuse is only detected later, in hist_register_trigger(). In the named-data branch hist_register_trigger() then frees the second histogram's hist_data via destroy_hist_data(), but never removes its tr->hist_vars list entry, leaving a dangling pointer and leaking the trace_array reference it holds. A later hist trigger that references a variable makes find_var_file() walk tr->hist_vars and dereference the freed hist_data. The bug is reproducible from userspace by writing three hist triggers to tracefs: cd /sys/kernel/tracing echo 'hist:keys=common_pid:x=common_pid:name=mh' > events/sched/sched_switch/trigger echo 'hist:keys=common_pid:x=common_pid:name=mh' > events/sched/sched_process_fork/trigger echo 'hist:keys=common_pid:vals=$x' > events/sched/sched_process_exit/trigger The third write panics the kernel: BUG: KASAN: slab-use-after-free in find_var_file.part.0+0x272/0x290 Read of size 8 at addr ffff888001f8a0e0 by task sh/1 CPU: 1 UID: 0 PID: 1 Comm: sh Tainted: G D N Call Trace: find_var_file.part.0 find_event_var parse_atom parse_expr __create_val_field event_hist_trigger_parse trigger_process_regex event_trigger_write vfs_write ksys_write do_syscall_64 entry_SYSCALL_64_after_hwframe Allocated by task 1: event_hist_trigger_parse Freed by task 1: hist_register_trigger+0x618/0xa30 event_hist_trigger_parse The buggy address belongs to freed 2048-byte region Oops: general protection fault ... RIP: find_var_file.part.0 Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b Fix by removing the hist_data from tr->hist_vars and releasing the trace_array reference in the named-data branch of hist_register_trigger() before freeing the hist_data. Cc: stable@vger.kernel.org Fixes: 6f86bdeab633 ("tracing: Fix bad hist from corrupting named_triggers list") Link: https://patch.msgid.link/20260816100427.33642-3-sh_def@163.com Signed-off-by: Hui Su <sh_def@163.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> 
When two hist triggers on different events are registered with the same
name=, the second one reuses the first as named_data.  Both are added to
tr->hist_vars by save_hist_vars() during event_hist_trigger_parse(),
because save_hist_vars() is called before event_trigger_register() while
the named reuse is only detected later, in hist_register_trigger().

In the named-data branch hist_register_trigger() then frees the second
histogram's hist_data via destroy_hist_data(), but never removes its
tr->hist_vars list entry, leaving a dangling pointer and leaking the
trace_array reference it holds.

A later hist trigger that references a variable makes find_var_file()
walk tr->hist_vars and dereference the freed hist_data.  The bug is
reproducible from userspace by writing three hist triggers to tracefs:

  cd /sys/kernel/tracing
  echo 'hist:keys=common_pid:x=common_pid:name=mh' > events/sched/sched_switch/trigger
  echo 'hist:keys=common_pid:x=common_pid:name=mh' > events/sched/sched_process_fork/trigger
  echo 'hist:keys=common_pid:vals=$x' > events/sched/sched_process_exit/trigger

The third write panics the kernel:

  BUG: KASAN: slab-use-after-free in find_var_file.part.0+0x272/0x290
  Read of size 8 at addr ffff888001f8a0e0 by task sh/1
  CPU: 1 UID: 0 PID: 1 Comm: sh Tainted: G      D          N
  Call Trace:
    find_var_file.part.0
    find_event_var
    parse_atom
    parse_expr
    __create_val_field
    event_hist_trigger_parse
    trigger_process_regex
    event_trigger_write
    vfs_write
    ksys_write
    do_syscall_64
    entry_SYSCALL_64_after_hwframe
  Allocated by task 1:
    event_hist_trigger_parse
  Freed by task 1:
    hist_register_trigger+0x618/0xa30
    event_hist_trigger_parse
  The buggy address belongs to freed 2048-byte region
  Oops: general protection fault ... RIP: find_var_file.part.0
  Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b

Fix by removing the hist_data from tr->hist_vars and releasing the
trace_array reference in the named-data branch of hist_register_trigger()
before freeing the hist_data.

Cc: stable@vger.kernel.org
Fixes: 6f86bdeab633 ("tracing: Fix bad hist from corrupting named_triggers list")
Link: https://patch.msgid.link/20260816100427.33642-3-sh_def@163.com
Signed-off-by: Hui Su <sh_def@163.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
tracing: Bound histogram expression strings with seq_buf 2026-07-28T11:18:49+00:00 Pengpeng Hou pengpeng@iscas.ac.cn 2026-06-11T05:59:45+00:00 935601a4276f28105498609f7f98aa66e86e9c96 expr_str() allocates a fixed MAX_FILTER_STR_VAL buffer and then builds expression names with a series of raw strcat() appends. Nested operands, constants, field flags, and generated field names can push the rendered string past that fixed limit before the name is attached to the hist field. Build expression strings with seq_buf and return -E2BIG when the rendered name would exceed MAX_FILTER_STR_VAL. This keeps the existing tracing-side limit while replacing the raw append logic with bounded construction. Link: https://patch.msgid.link/20260611055945.22348-4-pengpeng@iscas.ac.cn Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> 
expr_str() allocates a fixed MAX_FILTER_STR_VAL buffer and then builds
expression names with a series of raw strcat() appends. Nested operands,
constants, field flags, and generated field names can push the rendered
string past that fixed limit before the name is attached to the hist
field.

Build expression strings with seq_buf and return -E2BIG when the
rendered name would exceed MAX_FILTER_STR_VAL. This keeps the existing
tracing-side limit while replacing the raw append logic with bounded
construction.

Link: https://patch.msgid.link/20260611055945.22348-4-pengpeng@iscas.ac.cn
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
tracing: Return ERR_PTR() from expr_str() 2026-07-28T11:18:49+00:00 Pengpeng Hou pengpeng@iscas.ac.cn 2026-06-11T05:59:44+00:00 a5ca27e8ff1c10e949af7cfe474d6d1a08fb5601 expr_str() currently reports all failure cases as NULL, so callers cannot distinguish invalid recursion depth from allocation failure or later string construction errors. Return ERR_PTR()-encoded errors from expr_str() and make parse_unary() and parse_expr() propagate them. Clear expr->name before destroying the hist field so the error pointer is not freed as a string. Link: https://patch.msgid.link/20260611055945.22348-3-pengpeng@iscas.ac.cn Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> 
expr_str() currently reports all failure cases as NULL, so callers cannot
distinguish invalid recursion depth from allocation failure or later
string construction errors.

Return ERR_PTR()-encoded errors from expr_str() and make parse_unary()
and parse_expr() propagate them. Clear expr->name before destroying the
hist field so the error pointer is not freed as a string.

Link: https://patch.msgid.link/20260611055945.22348-3-pengpeng@iscas.ac.cn
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
tracing: Use __free() for expr_str() buffer 2026-07-28T11:18:49+00:00 Pengpeng Hou pengpeng@iscas.ac.cn 2026-06-11T05:59:43+00:00 988995c0552b6213b6bf16cea57258d4842c1488 expr_str() allocates a temporary expression buffer and manually frees it on some error paths. Convert the buffer to __free(kfree) and return it with return_ptr() on success. This keeps ownership handling separate from the later ERR_PTR() conversion and string-bound change. Link: https://patch.msgid.link/20260611055945.22348-2-pengpeng@iscas.ac.cn Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> 
expr_str() allocates a temporary expression buffer and manually frees it
on some error paths.

Convert the buffer to __free(kfree) and return it with return_ptr() on
success. This keeps ownership handling separate from the later ERR_PTR()
conversion and string-bound change.

Link: https://patch.msgid.link/20260611055945.22348-2-pengpeng@iscas.ac.cn
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
tracing: Point constant hist field type to string literal 2026-07-28T11:18:48+00:00 Yu Peng pengyu@kylinos.cn 2026-05-27T02:34:50+00:00 8432a8772bea4e0c142118421b89eaee3d5b2332 The HIST_FIELD_FL_CONST path uses the fixed "u64" type string. Point hist_field->type directly to the string literal, matching the HIST_FIELD_FL_HITCOUNT path. The release path already uses kfree_const(), so no duplication is needed. Link: https://patch.msgid.link/20260527023450.2137639-1-pengyu@kylinos.cn Signed-off-by: Yu Peng <pengyu@kylinos.cn> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> 
The HIST_FIELD_FL_CONST path uses the fixed "u64" type string.

Point hist_field->type directly to the string literal, matching the
HIST_FIELD_FL_HITCOUNT path. The release path already uses kfree_const(),
so no duplication is needed.

Link: https://patch.msgid.link/20260527023450.2137639-1-pengyu@kylinos.cn
Signed-off-by: Yu Peng <pengyu@kylinos.cn>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
tracing: Fix use-after-free freeing trigger private data 2026-07-24T22:49:51+00:00 David Carlier devnexen@gmail.com 2026-07-24T03:05:17+00:00 79097812153b826fc156a2930ec8a90ed9edf4a2 Commit 61d445af0a7c ("tracing: Add bulk garbage collection of freeing event_trigger_data") moved the kfree() of event_trigger_data to a kthread that runs tracepoint_synchronize_unregister() before freeing. That removed the synchronization the trigger .free callbacks used to get implicitly and inline from trigger_data_free(). event_hist_trigger_free(), event_hist_trigger_named_free() and event_enable_trigger_free() free their satellite data (hist_data, cmd_ops, enable_data) right after trigger_data_free() returns. With the synchronization now deferred to the kthread, a concurrent tracepoint handler can still reach that data through the list_del_rcu()'d trigger, causing a use-after-free. The histogram teardown must stay synchronous: remove_hist_vars() and unregister_field_var_hists() have to detach a synthetic event from the histogram before the trigger-removal write returns, otherwise a following command races in and the synthetic-event removal fails with -EBUSY, as the trigger-synthetic-eprobe.tc selftest catches. Make those callbacks wait with the correct barrier - tracepoint_synchronize_unregister(), matching the free kthread - before freeing. The enable trigger has no such synchronous requirement, and a blocking synchronize there would re-serialize the path that commit deliberately deferred. Give it an optional private_data_free() callback that the free kthread runs after its grace period, and free enable_data from there. Link: https://patch.msgid.link/20260724030523.19081-1-devnexen@gmail.com Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Suggested-by: Steven Rostedt <rostedt@goodmis.org> Fixes: 61d445af0a7c ("tracing: Add bulk garbage collection of freeing event_trigger_data") Signed-off-by: David Carlier <devnexen@gmail.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> 
Commit 61d445af0a7c ("tracing: Add bulk garbage collection of freeing
event_trigger_data") moved the kfree() of event_trigger_data to a kthread
that runs tracepoint_synchronize_unregister() before freeing. That removed
the synchronization the trigger .free callbacks used to get implicitly and
inline from trigger_data_free().

event_hist_trigger_free(), event_hist_trigger_named_free() and
event_enable_trigger_free() free their satellite data (hist_data, cmd_ops,
enable_data) right after trigger_data_free() returns. With the
synchronization now deferred to the kthread, a concurrent tracepoint
handler can still reach that data through the list_del_rcu()'d trigger,
causing a use-after-free.

The histogram teardown must stay synchronous: remove_hist_vars() and
unregister_field_var_hists() have to detach a synthetic event from the
histogram before the trigger-removal write returns, otherwise a following
command races in and the synthetic-event removal fails with -EBUSY, as the
trigger-synthetic-eprobe.tc selftest catches. Make those callbacks wait
with the correct barrier - tracepoint_synchronize_unregister(), matching
the free kthread - before freeing.

The enable trigger has no such synchronous requirement, and a blocking
synchronize there would re-serialize the path that commit deliberately
deferred. Give it an optional private_data_free() callback that the free
kthread runs after its grace period, and free enable_data from there.

Link: https://patch.msgid.link/20260724030523.19081-1-devnexen@gmail.com
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Fixes: 61d445af0a7c ("tracing: Add bulk garbage collection of freeing event_trigger_data")
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
tracing: Turn hist_elt_data field_var_str into a flexible array 2026-05-29T15:20:47+00:00 Rosen Penev rosenp@gmail.com 2026-05-22T21:44:07+00:00 bfda3b9424e02c6b2afac74410457c9c1743ba4a The field_var_str array was allocated separately via kcalloc() with its length already known at elt_data allocation time. Convert it to a flexible array member and fold the two allocations into a single kzalloc_flex(), reordering hist_trigger_elt_data_alloc() so n_str is computed and bounds-checked before the struct allocation. hist_elt_data is only reached through tracing_map_elt::private_data (a void *), never embedded, so adding a FAM imposes no tail-position constraint on any enclosing struct. Added __counted_by for extra runtime analysis. Link: https://patch.msgid.link/20260522214407.18120-1-rosenp@gmail.com Assisted-by: Claude:Opus-4.7 Signed-off-by: Rosen Penev <rosenp@gmail.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> 
The field_var_str array was allocated separately via kcalloc() with its
length already known at elt_data allocation time.  Convert it to a
flexible array member and fold the two allocations into a single
kzalloc_flex(), reordering hist_trigger_elt_data_alloc() so n_str is
computed and bounds-checked before the struct allocation.

hist_elt_data is only reached through tracing_map_elt::private_data
(a void *), never embedded, so adding a FAM imposes no tail-position
constraint on any enclosing struct.

Added __counted_by for extra runtime analysis.

Link: https://patch.msgid.link/20260522214407.18120-1-rosenp@gmail.com
Assisted-by: Claude:Opus-4.7
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
tracing: Bound synthetic-field strings with seq_buf 2026-05-21T22:03:06+00:00 Pengpeng Hou pengpeng@iscas.ac.cn 2026-04-30T04:33:50+00:00 f07883450eb14d1cf020b55d9f3a7ec5683bcd26 The synthetic field helpers build a prefixed synthetic variable name and a generated hist command in fixed MAX_FILTER_STR_VAL buffers. The current code appends those strings with raw strcat(), so long key lists, field names, or saved filters can run past the end of the staging buffers. Build both strings with seq_buf and propagate -E2BIG if either the synthetic variable name or the generated command exceeds MAX_FILTER_STR_VAL. This keeps the existing tracing-side limit while using the helper intended for bounded command construction. Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Tom Zanussi <tom.zanussi@linux.intel.com> Link: https://patch.msgid.link/20260430043350.57928-1-pengpeng@iscas.ac.cn Fixes: 02205a6752f2 ("tracing: Add support for 'field variables'") Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Reviewed-by: Tom Zanussi <zanussi@kernel.org> Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn> [ sdr: Moved struct seq_buf *s for upside-down x-mas tree formatting ] Signed-off-by: Steven Rostedt <rostedt@goodmis.org> 
The synthetic field helpers build a prefixed synthetic variable name and
a generated hist command in fixed MAX_FILTER_STR_VAL buffers. The
current code appends those strings with raw strcat(), so long key lists,
field names, or saved filters can run past the end of the staging
buffers.

Build both strings with seq_buf and propagate -E2BIG if either the
synthetic variable name or the generated command exceeds
MAX_FILTER_STR_VAL. This keeps the existing tracing-side limit while
using the helper intended for bounded command construction.

Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Link: https://patch.msgid.link/20260430043350.57928-1-pengpeng@iscas.ac.cn
Fixes: 02205a6752f2 ("tracing: Add support for 'field variables'")
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
[ sdr: Moved struct seq_buf *s for upside-down x-mas tree formatting ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
tracing: Avoid NULL return from hist_field_name() on truncation 2026-05-20T20:10:56+00:00 David Carlier devnexen@gmail.com 2026-05-08T19:57:47+00:00 576ec047d20b368b43c4d5db98c4f2e0f3c101ec hist_field_name() returns "" everywhere except the fully-qualified VAR_REF/EXPR case, where snprintf() truncation returns NULL early and bypasses the bottom NULL->"" guard. Callers don't expect NULL: strcat(expr, hist_field_name(field, 0)) at trace_events_hist.c:1758 and the strcmp() in the sort-key match loop at :4804 both deref it. system and event_name are bounded by MAX_EVENT_NAME_LEN, but the field name on a VAR_REF is kstrdup'd from a histogram variable name parsed out of the trigger string and has no length cap, so a long enough var name in a fully qualified reference can reach the truncation path. Keep the length check but leave field_name as "" on overflow. Link: https://patch.msgid.link/20260508195747.25492-1-devnexen@gmail.com Fixes: 5ec1d1e97de1 ("tracing: Rebuild full_name on each hist_field_name() call") Signed-off-by: David Carlier <devnexen@gmail.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> 
hist_field_name() returns "" everywhere except the fully-qualified
VAR_REF/EXPR case, where snprintf() truncation returns NULL early
and bypasses the bottom NULL->"" guard. Callers don't expect NULL:
strcat(expr, hist_field_name(field, 0)) at trace_events_hist.c:1758
and the strcmp() in the sort-key match loop at :4804 both deref it.

system and event_name are bounded by MAX_EVENT_NAME_LEN, but the
field name on a VAR_REF is kstrdup'd from a histogram variable
name parsed out of the trigger string and has no length cap, so
a long enough var name in a fully qualified reference can reach
the truncation path.

Keep the length check but leave field_name as "" on overflow.

Link: https://patch.msgid.link/20260508195747.25492-1-devnexen@gmail.com
Fixes: 5ec1d1e97de1 ("tracing: Rebuild full_name on each hist_field_name() call")
Signed-off-by: David Carlier <devnexen@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
tracing: Fix fully-qualified variable reference printing in histograms 2026-04-14T09:28:10+00:00 Tom Zanussi zanussi@kernel.org 2026-04-13T22:35:37+00:00 9236eebd138aa2753f7b30fc6cee7b7202841247 The syntax for fully-qualified variable references in histograms is subsys.event.$var, which is parsed correctly, but not displayed correctly when printing a histogram spec. The current code puts the $ reference at the beginning of the fully-qualified variable name i.e. $subsys.event.var, which is incorrect. Before: trigger info: hist:keys=next_comm:vals=hitcount:wakeup_lat=common_timestamp.usecs-$sched.sched_wakeup.ts0: ... After: trigger info: hist:keys=next_comm:vals=hitcount:wakeup_lat=common_timestamp.usecs-sched.sched_wakeup.$ts0: ... Link: https://patch.msgid.link/5dee9a86d062a4dd68c2214f3d90ac93811e1951.1776112478.git.zanussi@kernel.org Signed-off-by: Tom Zanussi <zanussi@kernel.org> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> 
The syntax for fully-qualified variable references in histograms is
subsys.event.$var, which is parsed correctly, but not displayed correctly
when printing a histogram spec. The current code puts the $ reference at
the beginning of the fully-qualified variable name i.e. $subsys.event.var,
which is incorrect.

Before:

trigger info: hist:keys=next_comm:vals=hitcount:wakeup_lat=common_timestamp.usecs-$sched.sched_wakeup.ts0: ...

After:

trigger info: hist:keys=next_comm:vals=hitcount:wakeup_lat=common_timestamp.usecs-sched.sched_wakeup.$ts0: ...

Link: https://patch.msgid.link/5dee9a86d062a4dd68c2214f3d90ac93811e1951.1776112478.git.zanussi@kernel.org
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>