Bug 8998 - ceph: prevent use-after-free in encode_cap_msg()
Summary: ceph: prevent use-after-free in encode_cap_msg()
Status: RESOLVED FIXED
Alias: None
Product: ANCK 5.10 Dev
Classification: ANCK
Component: fs (show other bugs) fs
Version: unspecified
Hardware: All Linux
: P3-Medium S3-normal
Target Milestone: ---
Assignee: benjma
QA Contact: shuming
URL:
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Keywords:
Depends on:
Blocks:
 
Reported: 2024-05-10 18:08 UTC by benjma
Modified: 2024-05-11 18:51 UTC (History)
3 users (show)

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Description benjma 2024-05-10 18:08:47 UTC 
Description of problem:

mainline inclusion
from mainline-v6.9-rc7

commit: cda4672da1c26835dcbd7aec2bfed954eda9b5ef

In fs/ceph/caps.c, in encode_cap_msg(), "use after free" error was
caught by KASAN at this line - 'ceph_buffer_get(arg->xattr_buf);'. This
implies before the refcount could be increment here, it was freed.

In same file, in "handle_cap_grant()" refcount is decremented by this
line - 'ceph_buffer_put(ci->i_xattrs.blob);'. It appears that a race
occurred and resource was freed by the latter line before the former
line could increment it.

encode_cap_msg() is called by __send_cap() and __send_cap() is called by
ceph_check_caps() after calling __prep_cap(). __prep_cap() is where
arg->xattr_buf is assigned to ci->i_xattrs.blob. This is the spot where
the refcount must be increased to prevent "use after free" error.

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v6.9-rc7&id=cda4672da1c26835dcbd7aec2bfed954eda9b5ef