The fields of a probe-based dynamic event (kprobe, uprobe, eprobe and
fprobe events) are created in traceprobe_define_arg_fields() by handing
the probe_arg name/type strings to trace_define_field(), which only
stores the pointers without copying. Those strings are owned by the
trace_probe and are freed when that probe is removed.

An event can have several probes attached. The field list is defined
only once, by the first probe that registers the event, but it is kept
alive by any surviving sibling probe. Deleting just that first probe by
symbol -

  # primary A: fields are defined from A's args
  echo 'p:kprobes/ev vfs_read  a1=$arg1' >  kprobe_events
  # append B: shares A's event call
  echo 'p:kprobes/ev vfs_write a1=$arg1' >> kprobe_events
  # delete only A (matched by symbol), B survives
  echo '-:kprobes/ev vfs_read'           >> kprobe_events

frees A's args (trace_probe_cleanup() -> traceprobe_free_probe_arg()),
but trace_probe_unlink() keeps the trace_probe_event because the probe
list is not empty. The event call stays registered via B while its
fields now reference freed memory. Any field lookup then reads it, e.g.

  echo 'a1 == 1' > events/kprobes/ev/filter

  BUG: KASAN: slab-use-after-free in strcmp+0xa7/0xb0
  Call Trace:
   strcmp
   trace_find_event_field
   parse_pred
   process_preds
   create_filter
   apply_event_filter
   event_filter_write

field->name references parg->name (kstrdup'd, freed with the probe) and,
for array arguments, field->type references parg->fmt (kmalloc'd, freed
with the probe) - the scalar type otherwise points at the static
fmttype rodata, which is safe.

Have traceprobe_define_arg_fields() duplicate the name and type strings
and anchor the copies on the trace_probe_event, which embeds the event
call and outlives every individual probe; trace_probe_event_free()
releases them.

The reproducer above triggers reliably; the field lookup and the delete
both run under event_mutex, so this is a dangling reference after
removal rather than a race.

The issue was found by the autokbug dynamic kernel fuzzer at Tencent
Yunding Lab.

Link: https://lore.kernel.org/all/20260826030009.1855331-1-bsdhenrymartin@gmail.com/

Fixes: ca89bc071d5e4 ("tracing/kprobe: Add multi-probe per event support")
Signed-off-by: Henry Martin <bsdhenrymartin@gmail.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Fix code block indentation introduced by commit f21834524025
("tracing/probes: Support field specifier option for typecast").

Link: https://lore.kernel.org/all/178827252027.123716.7095571176291547259.stgit@devnote2/

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>

btf_find_struct_member() traverses into nested anonymous structures and
unions to find a struct member. However, get_bitoffset_of_field() in
trace_probe.c checked btf_type_kflag(type) using the outer parent type
instead of the actual anonymous structure/union that directly contains
the found member.

If the parent structure and anonymous structure have mismatched kflags
(e.g., the parent has kflag=0 while the anonymous structure has kflag=1
because it contains bitfields), the bitfield size encoded in the upper
8 bits of member->offset is erroneously treated as part of the byte/bit
offset, corrupting the resolved offset and failing to set last_bitsize.
Similarly, btf_find_struct_member() pushed anonymous member offsets
onto anon_stack without masking BTF_MEMBER_BIT_OFFSET() when kflag is set.

To fix this problem, update btf_find_struct_member() to return actual
containing structure/union type via member_type, use appropriate
__btf_member_bit_offset() to get bit offset, and use member_type for
btf_type_kflag() in get_bitoffset_of_field().

Link: https://lore.kernel.org/all/178827250904.123716.17452648791331881284.stgit@devnote2/

Fixes: c440adfbe302 ("tracing/probes: Support BTF based data structure field access")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/all/20260822095110.0772E1F000E9@smtp.kernel.org/
Assisted-by: Antigravity:gemini-3.7-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>

Pull probes updates from Masami Hiramatsu:
 "BTF typecasting and variable fetch enhancements:

   - Typecast support across probe events: Extended BTF typecasting
     syntax (e.g., (STRUCT)PARAM->MEMBER) to kprobes, uprobes, and
     fprobes on function entry and return

   - Nested typecasts: Added support for chaining and nesting typecasts
     up to 3 levels, including casting registers and stack variables

   - Field specifier option: Added (STRUCT,FIELD) syntax to emulate
     container_of(), allowing retrieval of parent structures from member
     pointers

   - $current variable support: Introduced $current special variable to
     access the running task_struct via BTF dereferencing

   - Per-CPU variable access: Added this_cpu_read() and this_cpu_ptr()
     fetcharg methods to trace CPU-local data safely

   - Fetcharg bytecode dumper: Added CONFIG_PROBE_EVENTS_DUMP_FETCHARG
     to dump the compiled fetcharg bytecode instructions as comments in
     dynamic_events

   - Extended symbol name handling: Removed the MAX_COMMON_HEAD_LEN
     limit and extended MAX_ARGSTR_LEN to 256 bytes, enabling probing of
     long symbols, mangled Rust symbols and complex BTF expressions

   - eprobe variable syntax: Allowed eprobes to reference event fields
     directly without requiring a '$' prefix

   - Cleanup unused parameters, redundant codes, duplicate macros and
     pointer arithmetic

   - Use a ternary operator for simplifying fetch_type_from_btf_type()

  Expanded boot time dynamic probe support:

   - Add boot-time tracing configuration support for event probes
     (eprobes), function probes (fprobes), and tracepoint probes
     (tprobes)

   - Allow comment lines ('#') in dynamic_events file

  Optimization, robustness, and cleanups:

   - Simplify fprobe_remove_ips() by reusing graph and ftrace helpers

   - Remove __packed attribute from struct __fprobe_header to avoid
     unaligned memory access penalties on RISC architectures

   - Remove redundant memset() calls in perf event probe handlers

   - Replace legacy __ASSEMBLY__ with __ASSEMBLER__ in header files

  Selftests & refactoring:

   - Refactor parse_probe_arg() and parse_probe_vars(), and eliminate
     recursion in probe argument parsing to protect kernel stack depth

   - Add selftests for BTF typecasts and module probing without module
     prefixes

   - Force LC_ALL=C in ftracetest to prevent test failures on localized
     systems

   - Refactor btf_type_skip_modifiers() to remove ignored id parameter

   - Sort ERRORS list in trace_probe.h alphabetically

   - Fix typo in fprobe docs, and trace_fprobe function name

   - Rename FETCH_OP_DATA to FETCH_OP_IMMSTR

   - Make file offset error message probe-agnostic"

* tag 'probes-v7.3' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (37 commits)
  fprobe: Simplify fprobe_remove_ips() by reusing existing helpers
  tracing/boot: Add support for eprobe, fprobe, and tprobe events
  selftests/ftrace: Force C locale in ftracetest
  tracing/probes: Treating longer symbol name on event comparation
  docs: trace: fprobe: fix 'thos' spelling
  tracing/probes: Fix extra whitespace in trace_probe_kernel.h
  tracing/kprobe: Remove redundant memset in kprobe_perf_func()
  tracing/fprobe: Remove redundant memset in fentry_perf_func()
  tracing/fprobe: Remove redundant snprintf in trace_fprobe_match_command_head()
  tracing/probes: Simplify BTF_KIND_PTR case in fetch_type_from_btf_type()
  tracing/probes: Cleanup pointer arithmetic in store_trace_entry_data()
  tracing/probes: Remove unused parameter from parse_probe_var_retval()
  tracing/probes: Remove redundant bounds check in trace_probe_compare_arg_type()
  tracing/probes: Remove redundant boolean conversion in trace_probe_has_single_file()
  tracing/probes: Remove duplicate MAX_ARRAY_LEN macro definition
  selftests/ftrace: Add test case for a symbol in a module without module name
  tracing/probes: Eliminate recursion in parse_probe_arg()
  tracing/probes: Extend max length of argument string
  tracing/probes: Sort ERRORS list in trace_probe.h alphabetically
  tracing/probes: Refactor parse_probe_arg()
  ...

traceprobe_expand_meta_args() parses $argN with simple_strtoul() and
calls sprint_nth_btf_arg(n - 1, ...). For $arg0, n is 0 so the index is
-1. Because ctx->nr_params is signed, the "idx >= nr_params" guard in
sprint_nth_btf_arg() does not catch the negative index, and
ctx->params[-1].name_off is read out of bounds.

The normal per-argument path (parse_probe_vars()) already rejects
$arg0 via its argument-number check, but meta-argument expansion runs
before per-argument parsing and substitutes the value first, bypassing
that check.

Reject $arg0 explicitly during expansion.

Link: https://lore.kernel.org/all/20260724054435.146279-1-raushan.jhon@gmail.com/

Fixes: 18b1e870a496 ("tracing/probes: Add $arg* meta argument for all function args")
Cc: stable@vger.kernel.org
Signed-off-by: Raushan Patel <raushan.jhon@gmail.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Use a ternary operator for checking IS_ENABLED(CONFIG_64BIT) in the
BTF_KIND_PTR case of fetch_type_from_btf_type() to simplify the code.

Link: https://lore.kernel.org/all/178454426554.296567.17700307233923830044.stgit@devnote2/

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

In store_trace_entry_data(), edata is cast to unsigned long for pointer
offset arithmetic before being cast back to unsigned long *. Cast edata
to u8 * instead.

Link: https://lore.kernel.org/all/178454425622.296567.16952341966130280432.stgit@devnote2/

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

The parameter 'arg' in parse_probe_var_retval() is unused. Remove it
and update its caller accordingly.

Link: https://lore.kernel.org/all/178454424711.296567.15352344258939682112.stgit@devnote2/

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

In trace_probe_compare_arg_type(), prior to entering the comparison loop,
a->nr_args and b->nr_args are checked for equality. Since the loop
condition is i < a->nr_args, i is guaranteed to be less than b->nr_args
inside the loop.

Remove the redundant (b->nr_args <= i) check.

Link: https://lore.kernel.org/all/178454423769.296567.6694636865644203423.stgit@devnote2/

Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

In __set_print_fmt(), LEN_OR_ZERO is defined as (len ? len - pos : 0).
If len is non-zero but smaller than pos, len - pos evaluates to a negative
integer. When passed as a size argument to snprintf(), this negative value
is cast to a large unsigned size_t, bypassing buffer size limits.

Ensure len > pos before subtracting to avoid integer underflow.

Link: https://lore.kernel.org/all/178454234934.290363.15247317871499514139.stgit@devnote2/

Fixes: 5bf652aaf46c ("tracing/probes: Integrate duplicate set_print_fmt()")
Cc: stable@vger.kernel.org
Assisted-by: Antigravity:gemini-3.5-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>