CVE-2026-99274

Description

In 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.

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Patch details

References

• MITRE
• NVD
• Launchpad
• Debian

Other references

• https://www.cve.org/CVERecord?id=CVE-2026-99274
• https://git.kernel.org/stable/c/4a426ca5be7e3dedbe76575b967db04fbf01136f
• https://git.kernel.org/stable/c/f5baa17a0f316c235d61623ac8e8fb32c2b3c0cc
• https://git.kernel.org/stable/c/31f6dbb29fe17fa9595c7e8b19fd92915b03a4ca