commit 088bf2ff5d12e2e32ee52a4024fec26e582f44d3 upstream.
seq_read() is a nasty piece of work, not to mention buggy.
It has (I think) an old bug which allows unprivileged userspace to read
beyond the end of m->buf.
I was getting these:
BUG: KASAN: slab-out-of-bounds in seq_read+0xcd2/0x1480 at addr ffff880116889880
Read of size 2713 by task trinity-c2/1329
CPU: 2 PID: 1329 Comm: trinity-c2 Not tainted 4.8.0-rc1+ #96
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.9.3-0-ge2fc41e-prebuilt.qemu-project.org 04/01/2014
Call Trace:
kasan_object_err+0x1c/0x80
kasan_report_error+0x2cb/0x7e0
kasan_report+0x4e/0x80
check_memory_region+0x13e/0x1a0
kasan_check_read+0x11/0x20
seq_read+0xcd2/0x1480
proc_reg_read+0x10b/0x260
do_loop_readv_writev.part.5+0x140/0x2c0
do_readv_writev+0x589/0x860
vfs_readv+0x7b/0xd0
do_readv+0xd8/0x2c0
SyS_readv+0xb/0x10
do_syscall_64+0x1b3/0x4b0
entry_SYSCALL64_slow_path+0x25/0x25
Object at ffff880116889100, in cache kmalloc-4096 size: 4096
Allocated:
PID = 1329
save_stack_trace+0x26/0x80
save_stack+0x46/0xd0
kasan_kmalloc+0xad/0xe0
__kmalloc+0x1aa/0x4a0
seq_buf_alloc+0x35/0x40
seq_read+0x7d8/0x1480
proc_reg_read+0x10b/0x260
do_loop_readv_writev.part.5+0x140/0x2c0
do_readv_writev+0x589/0x860
vfs_readv+0x7b/0xd0
do_readv+0xd8/0x2c0
SyS_readv+0xb/0x10
do_syscall_64+0x1b3/0x4b0
return_from_SYSCALL_64+0x0/0x6a
Freed:
PID = 0
(stack is not available)
Memory state around the buggy address:
ffff88011688a000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88011688a080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88011688a100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88011688a180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88011688a200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
Disabling lock debugging due to kernel taint
This seems to be the same thing that Dave Jones was seeing here:
https://lkml.org/lkml/2016/8/12/334
There are multiple issues here:
1) If we enter the function with a non-empty buffer, there is an attempt
to flush it. But it was not clearing m->from after doing so, which
means that if we try to do this flush twice in a row without any call
to traverse() in between, we are going to be reading from the wrong
place -- the splat above, fixed by this patch.
2) If there's a short write to userspace because of page faults, the
buffer may already contain multiple lines (i.e. pos has advanced by
more than 1), but we don't save the progress that was made so the
next call will output what we've already returned previously. Since
that is a much less serious issue (and I have a headache after
staring at seq_read() for the past 8 hours), I'll leave that for now.
Link: http://lkml.kernel.org/r/1471447270-32093-1-git-send-email-vegard.nossum@oracle.com
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Once we'd freed m->buf, m->count should become zero - we have no valid contents reachable via m->buf. Reported-by: Charley (Hao Chuan) Chu <charley.chu@broadcom.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
There are several users who want to know bytes written by seq_*() for alignment purpose. Currently they are using %n format for knowing it because seq_*() returns 0 on success. This patch introduces seq_setwidth() and seq_pad() for allowing them to align without using %n format. Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Kees Cook <keescook@chromium.org> Cc: Joe Perches <joe@perches.com> Cc: David Miller <davem@davemloft.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This issue was first pointed out by Jiaxing Wang several months ago, but no
further comments:
https://lkml.org/lkml/2013/6/29/41
As we know pread() does not change f_pos, so after pread(), file->f_pos
and m->read_pos become different. And seq_lseek() does not update file->f_pos
if offset equals to m->read_pos, so after pread() and seq_lseek()(lseek to
m->read_pos), then a subsequent read may read from a wrong position, the
following program produces the problem:
char str1[32] = { 0 };
char str2[32] = { 0 };
int poffset = 10;
int count = 20;
/*open any seq file*/
int fd = open("/proc/modules", O_RDONLY);
pread(fd, str1, count, poffset);
printf("pread:%s\n", str1);
/*seek to where m->read_pos is*/
lseek(fd, poffset+count, SEEK_SET);
/*supposed to read from poffset+count, but this read from position 0*/
read(fd, str2, count);
printf("read:%s\n", str2);
out put:
pread:
ck_netbios_ns 12665
read:
nf_conntrack_netbios
/proc/modules:
nf_conntrack_netbios_ns 12665 0 - Live 0xffffffffa038b000
nf_conntrack_broadcast 12589 1 nf_conntrack_netbios_ns, Live 0xffffffffa0386000
So we always update file->f_pos to offset in seq_lseek() to fix this issue.
Signed-off-by: Jiaxing Wang <hello.wjx@gmail.com>
Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
When we convert the file_lock_list to a set of percpu lists, we'll need a way to iterate over them in order to output /proc/locks info. Add some seq_list_*_percpu helpers to handle that. Signed-off-by: Jeff Layton <jlayton@redhat.com> Acked-by: J. Bruce Fields <bfields@fieldses.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Same as single_open(), but preallocates the buffer of given size. Doesn't make any sense for sizes up to PAGE_SIZE and doesn't make sense if output of show() exceeds PAGE_SIZE only rarely - seq_read() will take care of growing the buffer and redoing show(). If you _know_ that it will be large, it might make more sense to look into saner iterator, rather than go with single-shot one. If that's impossible, single_open_size() might be for you. Again, don't use that without a good reason; occasionally that's really the best way to go, but very often there are better solutions. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Pull more VFS bits from Al Viro: "Unfortunately, it looks like xattr series will have to wait until the next cycle ;-/ This pile contains 9p cleanups and fixes (races in v9fs_fid_add() etc), fixup for nommu breakage in shmem.c, several cleanups and a bit more file_inode() work" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: constify path_get/path_put and fs_struct.c stuff fix nommu breakage in shmem.c cache the value of file_inode() in struct file 9p: if v9fs_fid_lookup() gets to asking server, it'd better have hashed dentry 9p: make sure ->lookup() adds fid to the right dentry 9p: untangle ->lookup() a bit 9p: double iput() in ->lookup() if d_materialise_unique() fails 9p: v9fs_fid_add() can't fail now v9fs: get rid of v9fs_dentry 9p: turn fid->dlist into hlist 9p: don't bother with private lock in ->d_fsdata; dentry->d_lock will do just fine more file_inode() open-coded instances selinux: opened file can't have NULL or negative ->f_path.dentry (In the meantime, the hlist traversal macros have changed, so this required a semantic conflict fixup for the newly hlistified fid->dlist)
[akpm@linux-foundation.org: checkpatch fixes] Cc: Cyrill Gorcunov <gorcunov@openvz.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>