When a BPF sock_ops program accesses ctx fields with dst_reg == src_reg,
the SOCK_OPS_GET_SK() and SOCK_OPS_GET_FIELD() macros fail to zero the
destination register in the !fullsock / !locked_tcp_sock path.
Both macros borrow a temporary register to check is_fullsock /
is_locked_tcp_sock when dst_reg == src_reg, because dst_reg holds the
ctx pointer. When the check is false (e.g., TCP_NEW_SYN_RECV state with
a request_sock), dst_reg should be zeroed but is not, leaving the stale
ctx pointer:
- SOCK_OPS_GET_SK: dst_reg retains the ctx pointer, passes NULL checks
as PTR_TO_SOCKET_OR_NULL, and can be used as a bogus socket pointer,
leading to stack-out-of-bounds access in helpers like
bpf_skc_to_tcp6_sock().
- SOCK_OPS_GET_FIELD: dst_reg retains the ctx pointer which the
verifier believes is a SCALAR_VALUE, leaking a kernel pointer.
Fix both macros by:
- Changing JMP_A(1) to JMP_A(2) in the fullsock path to skip the
added instruction.
- Adding BPF_MOV64_IMM(si->dst_reg, 0) after the temp register
restore in the !fullsock path, placed after the restore because
dst_reg == src_reg means we need src_reg intact to read ctx->temp.
Fixes: 84f44df664e9 ("bpf: sock_ops sk access may stomp registers when dst_reg
= src_reg")
Reported-by: Quan Sun <[email protected]>
Reported-by: Yinhao Hu <[email protected]>
Reported-by: Kaiyan Mei <[email protected]>
Reported-by: Dongliang Mu <[email protected]>
Closes:
https://lore.kernel.org/bpf/[email protected]/T/#u
Suggested-by: Emil Tsalapatis <[email protected]>
Signed-off-by: Jiayuan Chen <[email protected]>
---
---
net/core/filter.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index 78b548158fb05..53ce06ed4a88e 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -10581,10 +10581,11 @@ static u32 sock_ops_convert_ctx_access(enum
bpf_access_type type,
si->dst_reg, si->dst_reg, \
offsetof(OBJ, OBJ_FIELD)); \
if (si->dst_reg == si->src_reg) { \
- *insn++ = BPF_JMP_A(1); \
+ *insn++ = BPF_JMP_A(2); \
*insn++ = BPF_LDX_MEM(BPF_DW, reg, si->src_reg, \
offsetof(struct bpf_sock_ops_kern, \
temp)); \
+ *insn++ = BPF_MOV64_IMM(si->dst_reg, 0); \
} \
} while (0)
@@ -10618,10 +10619,11 @@ static u32 sock_ops_convert_ctx_access(enum
bpf_access_type type,
si->dst_reg, si->src_reg, \
offsetof(struct bpf_sock_ops_kern, sk));\
if (si->dst_reg == si->src_reg) { \
- *insn++ = BPF_JMP_A(1); \
+ *insn++ = BPF_JMP_A(2); \
*insn++ = BPF_LDX_MEM(BPF_DW, reg, si->src_reg, \
offsetof(struct bpf_sock_ops_kern, \
temp)); \
+ *insn++ = BPF_MOV64_IMM(si->dst_reg, 0); \
} \
} while (0)
--
2.43.0
