smb: client: validate dacloffset before building DACL pointers

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[ Upstream commit f98b48151c ]

parse_sec_desc(), build_sec_desc(), and the chown path in
id_mode_to_cifs_acl() all add the server-supplied dacloffset to pntsd
before proving a DACL header fits inside the returned security
descriptor.

On 32-bit builds a malicious server can return dacloffset near
U32_MAX, wrap the derived DACL pointer below end_of_acl, and then slip
past the later pointer-based bounds checks. build_sec_desc() and
id_mode_to_cifs_acl() can then dereference DACL fields from the wrapped
pointer in the chmod/chown rewrite paths.

Validate dacloffset numerically before building any DACL pointer and
reuse the same helper at the three DACL entry points.

Fixes: bc3e9dd9d1 ("cifs: Change SIDs in ACEs while transferring file ownership.")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
[ renamed smb_ntsd/smb_acl structs to cifs_ntsd/cifs_acl and kept existing inline ACL size check instead of using missing validate_dacl() helper ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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This commit is contained in:

Michael Bommarito 2026-05-16 15:09:10 -04:00 • committed by Greg Kroah-Hartman

parent 98b8104978

commit 5de2665e91

1 changed files with 32 additions and 3 deletions

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fs/cifs/cifsacl.c

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