smb: client: fix fiemap wild read on empty truncated response

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Summary

CVECVE-2026-99274
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-11-07 14:17:02 UTC
Updated2026-11-07 14:17:02 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: smb: client: fix fiemap wild read on empty truncated response smb3_fiemap() treats -E2BIG from SMB2_ioctl() as a truncated range blob and loops for the next chunk. If the server reports STATUS_BUFFER_OVERFLOW with OutputCount == 0, SMB2_ioctl() returns -E2BIG with out_data == NULL and out_data_len == 0, and the existing length checks accept the empty result. The loop then evaluates next = out_data[num - 1].file_offset + ... with num == 0, reading 16 bytes before NULL. Reject a truncated range blob that contains no range, so the resume offset is never computed from an empty response. Also require the last range in a truncated blob to advance the resume offset without overflowing, and to stay within the requested range; a malicious or broken server could otherwise make no progress or underflow len and loop forever. Free the previous response buffer before retrying. Reproduced on 6.6.87.2 with a malicious SMB2 server that answers FSCTL_QUERY_ALLOCATED_RANGES with STATUS_BUFFER_OVERFLOW and OutputCount == 0; an FS_IOC_FIEMAP ioctl on the mount oopses in cifs_fiemap() with CR2 = fffffffffffffff8. The code path is unchanged on mainline.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 2f3ebaba13cebd8badfb9aed31c0cf3cc82eb4f4 4a426ca5be7e3dedbe76575b967db04fbf01136f git Not specified
CNA Linux Linux affected 2f3ebaba13cebd8badfb9aed31c0cf3cc82eb4f4 31f6dbb29fe17fa9595c7e8b19fd92915b03a4ca git Not specified
CNA Linux Linux affected 2f3ebaba13cebd8badfb9aed31c0cf3cc82eb4f4 f5baa17a0f316c235d61623ac8e8fb32c2b3c0cc git Not specified
CNA Linux Linux affected 5.2 Not specified
CNA Linux Linux unaffected 5.2 semver Not specified
CNA Linux Linux unaffected 6.18.61 6.18.* semver Not specified
CNA Linux Linux unaffected 7.3.2 7.3.* semver Not specified
CNA Linux Linux unaffected 7.4-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/f5baa17a0f316c235d61623ac8e8fb32c2b3c0cc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/31f6dbb29fe17fa9595c7e8b19fd92915b03a4ca 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/4a426ca5be7e3dedbe76575b967db04fbf01136f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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