bpf: don't downgrade half-dead scalar zero spills to STACK_ZERO
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- Fix
- Fixed in 7.2.7
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: don't downgrade half-dead scalar zero spills to STACK_ZERO states.c:__clean_func_state() can downgrade scalar zero spill to STACK_ZERO in the following case: (u64 )(r10 - 8) = 0; ... checkpoint ... r1 = (u32 )(r10 - 4); ... no reads from r10-8 ... Here 4 bytes at r10-8 are dead and verifier changes scalar spill to a combination: 0000pppp (p stands for poison). Such a change breaks precision propagation chains. All places that produce STACK_ZERO should call bpf_mark_chain_precision() for the zero source. This patch fixes the bug in a simplest way possible: avoids converting stack spills of zero to STACK_ZERO. Two smarter approaches are possible: • do bpf_mark_chain_precision() from __clean_func_state() • check slot liveness information in check_stack_write_fixed_off() I investigated both and the changes required are a bit tricky, hence go with a simple fix for the time being.
Timeline
- CVE published
- Record last updated
Affected versions
- Linux Linux
From be23266b4a08540aa43d8503a2ea10247c8daebe · fixed in 436fa689630b741a77ef8c4a6f426479affd5bac; From be23266b4a08540aa43d8503a2ea10247c8daebe · fixed in 2f3536bff8823d3c5fdbbe15e17bfca696cc2b2e
- Linux Linux
7.1
- KernelLinux
From 7.1.0 · fixed in 7.2.7