CVE-2026-31613

In the Linux kernel, the following vulnerability has been resolved:

smb: client: fix OOB reads parsing symlink error response

When a CREATE returns STATUS_STOPPED_ON_SYMLINK, smb2_check_message()

returns success without any length validation, leaving the symlink

parsers as the only defense against an untrusted server.

symlink_data() walks SMB 3.1.1 error contexts with the loop test "p <

end", but reads p->ErrorId at offset 4 and p->ErrorDataLength at offset

0. When the server-controlled ErrorDataLength advances p to within 1-7

bytes of end, the next iteration will read past it. When the matching

context is found, sym->SymLinkErrorTag is read at offset 4 from

p->ErrorContextData with no check that the symlink header itself fits.

smb2_parse_symlink_response() then bounds-checks the substitute name

using SMB2_SYMLINK_STRUCT_SIZE as the offset of PathBuffer from

iov_base. That value is computed as sizeof(smb2_err_rsp) +

sizeof(smb2_symlink_err_rsp), which is correct only when

ErrorContextCount == 0.

With at least one error context the symlink data sits 8 bytes deeper,

and each skipped non-matching context shifts it further by 8 +

ALIGN(ErrorDataLength, 8). The check is too short, allowing the

substitute name read to run past iov_len. The out-of-bound heap bytes

are UTF-16-decoded into the symlink target and returned to userspace via

readlink(2).

Fix this all up by making the loops test require the full context header

to fit, rejecting sym if its header runs past end, and bound the

substitute name against the actual position of sym->PathBuffer rather

than a fixed offset.

Because sub_offs and sub_len are 16bits, the pointer math will not

overflow here with the new greater-than.