Bug 2541319 (CVE-2026-98126)

Summary: CVE-2026-98126 kernel: smb/client: validate new EOF for zero range
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's SMB client. This flaw allows a local user to bypass enforced file-size restrictions and expand files beyond authorized limits. When handling file allocation operations that zero out a range of data without preserving the file's existing size, the kernel fails to check whether the new size exceeds configured process file-size limits (RLIMIT_FSIZE). Consequently, a local user can write or extend files on mounted network shares beyond permitted resource boundaries.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-09-25 11:23:07 UTC 
In the Linux kernel, the following vulnerability has been resolved:

smb/client: validate new EOF for zero range

When FALLOC_FL_ZERO_RANGE is used without FALLOC_FL_KEEP_SIZE,
smb3_zero_range() may extend EOF without checking RLIMIT_FSIZE, allowing
the file to grow beyond the caller's file-size limit.

Fix this by calling inode_newsize_ok() before sending the zero-range
request when the operation would extend EOF.

Reproducer, using a file on a CIFS mount:

	bash -c '
	        FILE=/mnt/cifs/repro

	        trap "" SIGXFSZ
	        ulimit -f 3072

	        truncate -s 2M "$FILE"
	        fallocate --zero-range -o 0 -l 4M "$FILE"
	        echo "fallocate rc=$?"
	        stat -c "file size=%s" "$FILE"
	'

Before this change, the operation succeeds despite the 3 MiB limit:

	fallocate rc=0
	file size=4194304

After this change, fallocate fails and leaves the file at 2 MiB.
Comment 1 Keith Grant 2026-09-28 13:44:51 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98126.mbox