Description (CNA)
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix incorrect pruning due to atomic fetch precision tracking When backtrack_insn encounters a BPF_STX instruction with BPF_ATOMIC and BPF_FETCH, the src register (or r0 for BPF_CMPXCHG) also acts as a destination, thus receiving the old value from the memory location. The current backtracking logic does not account for this. It treats atomic fetch operations the same as regular stores where the src register is only an input. This leads the backtrack_insn to fail to propagate precision to the stack location, which is then not marked as precise! Later, the verifier's path pruning can incorrectly consider two states equivalent when they differ in terms of stack state. Meaning, two branches can be treated as equivalent and thus get pruned when they should not be seen as such. Fix it as follows: Extend the BPF_LDX handling in backtrack_insn to also cover atomic fetch operations via is_atomic_fetch_insn() helper. When the fetch dst register is being tracked for precision, clear it, and propagate precision over to the stack slot. For non-stack memory, the precision walk stops at the atomic instruction, same as regular BPF_LDX. This covers all fetch variants. Before: 0: (b7) r1 = 8 ; R1=8 1: (7b) *(u64 *)(r10 -8) = r1 ; R1=8 R10=fp0 fp-8=8 2: (b7) r2 = 0 ; R2=0 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2) ; R2=8 R10=fp0 fp-8=mmmmmmmm 4: (bf) r3 = r10 ; R3=fp0 R10=fp0 5: (0f) r3 += r2 mark_precise: frame0: last_idx 5 first_idx 0 subseq_idx -1 mark_precise: frame0: regs=r2 stack= before 4: (bf) r3 = r10 mark_precise: frame0: regs=r2 stack= before 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2) mark_precise: frame0: regs=r2 stack= before 2: (b7) r2 = 0 6: R2=8 R3=fp8 6: (b7) r0 = 0 ; R0=0 7: (95) exit After: 0: (b7) r1 = 8 ; R1=8 1: (7b) *(u64 *)(r10 -8) = r1 ; R1=8 R10=fp0 fp-8=8 2: (b7) r2 = 0 ; R2=0 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2) ; R2=8 R10=fp0 fp-8=mmmmmmmm 4: (bf) r3 = r10 ; R3=fp0 R10=fp0 5: (0f) r3 += r2 mark_precise: frame0: last_idx 5 first_idx 0 subseq_idx -1 mark_precise: frame0: regs=r2 stack= before 4: (bf) r3 = r10 mark_precise: frame0: regs=r2 stack= before 3: (db) r2 = atomic64_fetch_add((u64 *)(r10 -8), r2) mark_precise: frame0: regs= stack=-8 before 2: (b7) r2 = 0 mark_precise: frame0: regs= stack=-8 before 1: (7b) *(u64 *)(r10 -8) = r1 mark_precise: frame0: regs=r1 stack= before 0: (b7) r1 = 8 6: R2=8 R3=fp8 6: (b7) r0 = 0 ; R0=0 7: (95) exit
Affected (CNA)
| Vendor / product | Versions |
|---|---|
| Linux / Linux | affected 5ca419f2864a2c60940dcf4bbaeb69546200e36f before 1aac6b271e0a80b91c2f6a8f75ab0c0b1fc8ffe8; affected 5ca419f2864a2c60940dcf4bbaeb69546200e36f before 7c72e5f3741d1c5cc53439137162f0e09254e6e9; affected 5ca419f2864a2c60940dcf4bbaeb69546200e36f before ea150ffa9fc9f78c5cf22e1f7b06b6d016b1017c; affected 5ca419f2864a2c60940dcf4bbaeb69546200e36f before 7ffbe45b1d227e24659998a91cfd4c27af457e71; affected 5ca419f2864a2c60940dcf4bbaeb69546200e36f before 179ee84a89114b854ac2dd1d293633a7f6c8dac1 |
| Linux / Linux | affected 5.12; unaffected 0 before 5.12; unaffected 6.6.160 through 6.6.*; unaffected 6.12.114 through 6.12.*; unaffected 6.18.50 through 6.18.*; unaffected 6.19.12 through 6.19.*; unaffected 7.0 through * |
CWE
No CWE identifiers supplied.
References
- https://git.kernel.org/stable/c/1aac6b271e0a80b91c2f6a8f75ab0c0b1fc8ffe8
- https://git.kernel.org/stable/c/7c72e5f3741d1c5cc53439137162f0e09254e6e9
- https://git.kernel.org/stable/c/ea150ffa9fc9f78c5cf22e1f7b06b6d016b1017c
- https://git.kernel.org/stable/c/7ffbe45b1d227e24659998a91cfd4c27af457e71
- https://git.kernel.org/stable/c/179ee84a89114b854ac2dd1d293633a7f6c8dac1
ADP enrichment
No English description supplied.
No references supplied.