5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiayuan Chen [ Upstream commit 10f86a2a5c91fc4c4d001960f1c21abe52545ef6 ] 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: fd09af010788 ("bpf: sock_ops ctx access may stomp registers in corner case") Fixes: 84f44df664e9 ("bpf: sock_ops sk access may stomp registers when dst_reg = src_reg") Reported-by: Quan Sun <2022090917019@std.uestc.edu.cn> Reported-by: Yinhao Hu Reported-by: Kaiyan Mei Reported-by: Dongliang Mu Reviewed-by: Emil Tsalapatis Closes: https://lore.kernel.org/bpf/6fe1243e-149b-4d3b-99c7-fcc9e2f75787@std.uestc.edu.cn/T/#u Signed-off-by: Jiayuan Chen Acked-by: Martin KaFai Lau Link: https://patch.msgid.link/20260407022720.162151-2-jiayuan.chen@linux.dev Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- 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 8ec5b4d868ab9..0338dc0bf1e9b 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -9268,10 +9268,11 @@ 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) @@ -9305,10 +9306,11 @@ 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) -- 2.53.0