linux-stable.git/fs/seq_file.c, branch v3.2.100 Linux kernel stable tree fs/seq_file: fix out-of-bounds read 2016-11-20T01:01:35+00:00 Vegard Nossum vegard.nossum@oracle.com 2016-08-25T22:17:11+00:00 1335a3ab2dcc684c65caba15d36957ee816a0236 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: Ben Hutchings <ben@decadent.org.uk> 
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: Ben Hutchings <ben@decadent.org.uk>
fix apparmor dereferencing potentially freed dentry, sanitize __d_path() API 2011-12-07T04:57:18+00:00 Al Viro viro@zeniv.linux.org.uk 2011-12-05T13:43:34+00:00 02125a826459a6ad142f8d91c5b6357562f96615 __d_path() API is asking for trouble and in case of apparmor d_namespace_path() getting just that. The root cause is that when __d_path() misses the root it had been told to look for, it stores the location of the most remote ancestor in *root. Without grabbing references. Sure, at the moment of call it had been pinned down by what we have in *path. And if we raced with umount -l, we could have very well stopped at vfsmount/dentry that got freed as soon as prepend_path() dropped vfsmount_lock. It is safe to compare these pointers with pre-existing (and known to be still alive) vfsmount and dentry, as long as all we are asking is "is it the same address?". Dereferencing is not safe and apparmor ended up stepping into that. d_namespace_path() really wants to examine the place where we stopped, even if it's not connected to our namespace. As the result, it looked at ->d_sb->s_magic of a dentry that might've been already freed by that point. All other callers had been careful enough to avoid that, but it's really a bad interface - it invites that kind of trouble. The fix is fairly straightforward, even though it's bigger than I'd like: * prepend_path() root argument becomes const. * __d_path() is never called with NULL/NULL root. It was a kludge to start with. Instead, we have an explicit function - d_absolute_root(). Same as __d_path(), except that it doesn't get root passed and stops where it stops. apparmor and tomoyo are using it. * __d_path() returns NULL on path outside of root. The main caller is show_mountinfo() and that's precisely what we pass root for - to skip those outside chroot jail. Those who don't want that can (and do) use d_path(). * __d_path() root argument becomes const. Everyone agrees, I hope. * apparmor does *NOT* try to use __d_path() or any of its variants when it sees that path->mnt is an internal vfsmount. In that case it's definitely not mounted anywhere and dentry_path() is exactly what we want there. Handling of sysctl()-triggered weirdness is moved to that place. * if apparmor is asked to do pathname relative to chroot jail and __d_path() tells it we it's not in that jail, the sucker just calls d_absolute_path() instead. That's the other remaining caller of __d_path(), BTW. * seq_path_root() does _NOT_ return -ENAMETOOLONG (it's stupid anyway - the normal seq_file logics will take care of growing the buffer and redoing the call of ->show() just fine). However, if it gets path not reachable from root, it returns SEQ_SKIP. The only caller adjusted (i.e. stopped ignoring the return value as it used to do). Reviewed-by: John Johansen <john.johansen@canonical.com> ACKed-by: John Johansen <john.johansen@canonical.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Cc: stable@vger.kernel.org 
__d_path() API is asking for trouble and in case of apparmor d_namespace_path()
getting just that.  The root cause is that when __d_path() misses the root
it had been told to look for, it stores the location of the most remote ancestor
in *root.  Without grabbing references.  Sure, at the moment of call it had
been pinned down by what we have in *path.  And if we raced with umount -l, we
could have very well stopped at vfsmount/dentry that got freed as soon as
prepend_path() dropped vfsmount_lock.

It is safe to compare these pointers with pre-existing (and known to be still
alive) vfsmount and dentry, as long as all we are asking is "is it the same
address?".  Dereferencing is not safe and apparmor ended up stepping into
that.  d_namespace_path() really wants to examine the place where we stopped,
even if it's not connected to our namespace.  As the result, it looked
at ->d_sb->s_magic of a dentry that might've been already freed by that point.
All other callers had been careful enough to avoid that, but it's really
a bad interface - it invites that kind of trouble.

The fix is fairly straightforward, even though it's bigger than I'd like:
	* prepend_path() root argument becomes const.
	* __d_path() is never called with NULL/NULL root.  It was a kludge
to start with.  Instead, we have an explicit function - d_absolute_root().
Same as __d_path(), except that it doesn't get root passed and stops where
it stops.  apparmor and tomoyo are using it.
	* __d_path() returns NULL on path outside of root.  The main
caller is show_mountinfo() and that's precisely what we pass root for - to
skip those outside chroot jail.  Those who don't want that can (and do)
use d_path().
	* __d_path() root argument becomes const.  Everyone agrees, I hope.
	* apparmor does *NOT* try to use __d_path() or any of its variants
when it sees that path->mnt is an internal vfsmount.  In that case it's
definitely not mounted anywhere and dentry_path() is exactly what we want
there.  Handling of sysctl()-triggered weirdness is moved to that place.
	* if apparmor is asked to do pathname relative to chroot jail
and __d_path() tells it we it's not in that jail, the sucker just calls
d_absolute_path() instead.  That's the other remaining caller of __d_path(),
BTW.
        * seq_path_root() does _NOT_ return -ENAMETOOLONG (it's stupid anyway -
the normal seq_file logics will take care of growing the buffer and redoing
the call of ->show() just fine).  However, if it gets path not reachable
from root, it returns SEQ_SKIP.  The only caller adjusted (i.e. stopped
ignoring the return value as it used to do).

Reviewed-by: John Johansen <john.johansen@canonical.com>
ACKed-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: stable@vger.kernel.org
fs: take dcache_lock inside __d_path 2010-10-26T01:26:12+00:00 Christoph Hellwig hch@infradead.org 2010-10-10T09:36:21+00:00 be148247cfbe2422f5709e77d9c3e10b8a6394da All callers take dcache_lock just around the call to __d_path, so take the lock into it in preparation of getting rid of dcache_lock. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> 
All callers take dcache_lock just around the call to __d_path, so
take the lock into it in preparation of getting rid of dcache_lock.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
fs/seq_file.c: Remove unnecessary casts of private_data 2010-09-23T11:28:23+00:00 Joe Perches joe@perches.com 2010-09-05T01:52:49+00:00 8209e2f46752914e94f65469b8312c42dc5d7d8f Signed-off-by: Joe Perches <joe@perches.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz> 
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
seq_file: fix new kernel-doc warnings 2010-03-07T23:48:26+00:00 Randy Dunlap randy.dunlap@oracle.com 2010-03-04T17:37:12+00:00 138860b95359feee49a31fb12be87825e4cd84ac Fix kernel-doc notation in new seq-file functions and correct spelling. Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Cc: Li Zefan <lizf@cn.fujitsu.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> 
Fix kernel-doc notation in new seq-file functions and
correct spelling.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
seq_file: add RCU versions of new hlist/list iterators (v3) 2010-02-22T23:45:54+00:00 stephen hemminger shemminger@vyatta.com 2010-02-22T07:57:17+00:00 1cc523271ef0b6305c565a143e3d48f6fff826dd Many usages of seq_file use RCU protected lists, so non RCU iterators will not work safely. Signed-off-by: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
Many usages of seq_file use RCU protected lists, so non RCU
iterators will not work safely.

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
seq_file: Add helpers for iteration over a hlist 2010-02-10T19:12:06+00:00 Li Zefan lizf@cn.fujitsu.com 2010-02-08T23:18:22+00:00 66655de6d132b726be64c324bc3f9ea366d20697 Some places in kernel need to iterate over a hlist in seq_file, so provide some common helpers. Signed-off-by: Li Zefan <lizf@cn.fujitsu.com> Signed-off-by: David S. Miller <davem@davemloft.net> 
Some places in kernel need to iterate over a hlist in seq_file,
so provide some common helpers.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
vfs: seq_file: add helpers for data filling 2009-09-24T11:47:35+00:00 Miklos Szeredi mszeredi@suse.cz 2009-09-21T12:48:36+00:00 f84398068d9c2babe41500504ef247ae07081857 Add two helpers that allow access to the seq_file's own buffer, but hide the internal details of seq_files. This allows easier implementation of special purpose filling functions. It also cleans up some existing functions which duplicated the seq_file logic. Make these inline functions in seq_file.h, as suggested by Al. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> 
Add two helpers that allow access to the seq_file's own buffer, but
hide the internal details of seq_files.

This allows easier implementation of special purpose filling
functions.  It also cleans up some existing functions which duplicated
the seq_file logic.

Make these inline functions in seq_file.h, as suggested by Al.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
seq_file: return a negative error code when seq_path_root() fails. 2009-09-24T11:47:29+00:00 Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp 2009-09-18T20:05:59+00:00 7a62cc10215838286c747f86766063d5f01fcbd6 seq_path_root() is returning a return value of successful __d_path() instead of returning a negative value when mangle_path() failed. This is not a bug so far because nobody is using return value of seq_path_root(). Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> 
seq_path_root() is returning a return value of successful __d_path()
instead of returning a negative value when mangle_path() failed.

This is not a bug so far because nobody is using return value of
seq_path_root().

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
seq_file: add function to write binary data 2009-06-18T20:03:57+00:00 Peter Oberparleiter oberpar@linux.vnet.ibm.com 2009-06-17T23:28:05+00:00 0b923606e75f1ab672e25b14ac039a1cdcfa382f seq_write() can be used to construct seq_files containing arbitrary data. Required by the gcov-profiling interface to synthesize binary profiling data files. Signed-off-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com> Cc: Andi Kleen <andi@firstfloor.org> Cc: Huang Ying <ying.huang@intel.com> Cc: Li Wei <W.Li@Sun.COM> Cc: Michael Ellerman <michaele@au1.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Heiko Carstens <heicars2@linux.vnet.ibm.com> Cc: Martin Schwidefsky <mschwid2@linux.vnet.ibm.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: WANG Cong <xiyou.wangcong@gmail.com> Cc: Sam Ravnborg <sam@ravnborg.org> Cc: Jeff Dike <jdike@addtoit.com> 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> 
seq_write() can be used to construct seq_files containing arbitrary data.
Required by the gcov-profiling interface to synthesize binary profiling
data files.

Signed-off-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Li Wei <W.Li@Sun.COM>
Cc: Michael Ellerman <michaele@au1.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Heiko Carstens <heicars2@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <mschwid2@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: WANG Cong <xiyou.wangcong@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Jeff Dike <jdike@addtoit.com>
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>