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fix stack buffer overflow in SaveAsFile backup path construction - #6420
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larsewi
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Oct 19, 2026
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Please remove the test. The fix is easy enough to verify by reading it. And the test tests a side effect, not the behavior. Otherwise LGTM, thanks 🚀
Signed-off-by: Dhanraj E <dhanraj@labs.digiscrypt.com>
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Dropped the unit test and the |
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@cf-bottom Jenkins please :) |
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Alright, I triggered a build: Jenkins: https://ci.cfengine.com/job/pr-pipeline/14827/ Packages: http://buildcache.cfengine.com/packages/testing-pr/jenkins-pr-pipeline-14827/ |
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Repro: run an
edit_line(oredit_xml) files promise whose promiser is a symlink pointing to a target path nearCF_BUFSIZElong;cf-agentcrashes (ASan: stack-buffer-overflow inSaveAsFile).Cause: after
SaveAsFile()dereferences the symlink chain intoderef_file(aBuffer, so up toCF_BUFSIZE), it builds the.cf-before-editbackup name and.cf-after-edittemp name withstrcpy()/strcat()into the fixedbackup[CF_BUFSIZE]andnew[CF_BUFSIZE]stack buffers, plus a timestamp. A dereferenced path close toCF_BUFSIZEoverruns both buffers. Reached from any files promise withedit_line/edit_xmlviaFinishEditContext->SaveItemListAsFile->SaveAsFile.Fix: use
strlcpy/strlcatand refuse the edit (as the function already does on other failures) when the backup/temp name would not fit, matching the bounded copies already used a few lines above in this file.Verified with AddressSanitizer: a unit test in
tests/unit/files_operators_test.c(drivingSaveItemListAsFileover a long symlink target) and a realcf-agentedit_line run both trip the overflow before the change and are clean after. Full unit suite stays green under-fsanitize=address.