[PATCH 7.2.y 2/2] tracing/probes: Fix BTF kflag check for anonymous struct member access
From: Sasha Levin <sashal@kernel.org>
Date: 2026-09-10 11:47:04
Subsystem:
the rest, tracing · Maintainers:
Linus Torvalds, Steven Rostedt, Masami Hiramatsu
From: "Masami Hiramatsu (Google)" <mhiramat@kernel.org> [ Upstream commit 47e93045a2db80d24f5fef65adecc6b2b32efa23 ] btf_find_struct_member() traverses into nested anonymous structures and unions to find a struct member. However, get_bitoffset_of_field() in trace_probe.c checked btf_type_kflag(type) using the outer parent type instead of the actual anonymous structure/union that directly contains the found member. If the parent structure and anonymous structure have mismatched kflags (e.g., the parent has kflag=0 while the anonymous structure has kflag=1 because it contains bitfields), the bitfield size encoded in the upper 8 bits of member->offset is erroneously treated as part of the byte/bit offset, corrupting the resolved offset and failing to set last_bitsize. Similarly, btf_find_struct_member() pushed anonymous member offsets onto anon_stack without masking BTF_MEMBER_BIT_OFFSET() when kflag is set. To fix this problem, update btf_find_struct_member() to return actual containing structure/union type via member_type, use appropriate __btf_member_bit_offset() to get bit offset, and use member_type for btf_type_kflag() in get_bitoffset_of_field(). Link: https://lore.kernel.org/all/178827250904.123716.17452648791331881284.stgit@devnote2/ (local) Fixes: c440adfbe302 ("tracing/probes: Support BTF based data structure field access") Cc: stable@vger.kernel.org Reported-by: Sashiko <sashiko-bot@kernel.org> Closes: https://lore.kernel.org/all/20260822095110.0772E1F000E9@smtp.kernel.org/ (local) Assisted-by: Antigravity:gemini-3.7-flash Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> [ applied changes to parse_btf_field() because get_bitoffset_of_field() is absent. ] Signed-off-by: Sasha Levin <sashal@kernel.org> --- kernel/trace/trace_btf.c | 19 +++++++++++-------- kernel/trace/trace_btf.h | 3 ++- kernel/trace/trace_probe.c | 5 +++-- 3 files changed, 16 insertions(+), 11 deletions(-)
diff --git a/kernel/trace/trace_btf.c b/kernel/trace/trace_btf.c
index 00172f301f25a..33de9b80118cf 100644
--- a/kernel/trace/trace_btf.c
+++ b/kernel/trace/trace_btf.c@@ -61,16 +61,17 @@ struct btf_anon_stack { /* * Find a member of data structure/union by name and return it. - * Return NULL if not found, or -EINVAL if parameter is invalid. - * If the member is an member of anonymous union/structure, the offset - * of that anonymous union/structure is stored into @anon_offset. Caller - * can calculate the correct offset from the root data structure by - * adding anon_offset to the member's offset. + * Return NULL if not found, or ERR_PTR(-EINVAL) if parameter is invalid. + * If the member is a member of an anonymous union/structure, the bit offset + * of that anonymous union/structure is stored into @anon_offset. + * If @member_type is non-NULL, the actual containing structure/union type + * of the found member is stored into @member_type. */ const struct btf_member *btf_find_struct_member(struct btf *btf, const struct btf_type *type, const char *member_name, - u32 *anon_offset) + u32 *anon_offset, + const struct btf_type **member_type) { struct btf_anon_stack *anon_stack; const struct btf_member *member;
@@ -94,14 +95,16 @@ const struct btf_member *btf_find_struct_member(struct btf *btf, if (btf_type_skip_modifiers(btf, member->type, &tid) && top < BTF_ANON_STACK_MAX) { anon_stack[top].tid = tid; - anon_stack[top++].offset = - cur_offset + member->offset; + anon_stack[top++].offset = cur_offset + + __btf_member_bit_offset(type, member); } } else { name = btf_name_by_offset(btf, member->name_off); if (name && !strcmp(member_name, name)) { if (anon_offset) *anon_offset = cur_offset; + if (member_type) + *member_type = type; goto out; } }
diff --git a/kernel/trace/trace_btf.h b/kernel/trace/trace_btf.h
index 4bc44bc261e6f..4bd26bceae23a 100644
--- a/kernel/trace/trace_btf.h
+++ b/kernel/trace/trace_btf.h@@ -8,4 +8,5 @@ const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, const struct btf_member *btf_find_struct_member(struct btf *btf, const struct btf_type *type, const char *member_name, - u32 *anon_offset); + u32 *anon_offset, + const struct btf_type **member_type);
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 2d58cf99b6f70..aae60fbebeafb 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c@@ -578,6 +578,7 @@ static int parse_btf_field(char *fieldname, const struct btf_type *type, { struct fetch_insn *code = *pcode; const struct btf_member *field; + const struct btf_type *mtype; u32 bitoffs, anon_offs; bool is_struct = ctx->struct_btf != NULL; struct btf *btf = ctx_btf(ctx);
@@ -612,7 +613,7 @@ static int parse_btf_field(char *fieldname, const struct btf_type *type, anon_offs = 0; field = btf_find_struct_member(btf, type, fieldname, - &anon_offs); + &anon_offs, &mtype); if (IS_ERR(field)) { trace_probe_log_err(ctx->offset, BAD_BTF_TID); return PTR_ERR(field);
@@ -625,7 +626,7 @@ static int parse_btf_field(char *fieldname, const struct btf_type *type, bitoffs += anon_offs; /* Accumulate the bit-offsets of the dot-connected fields */ - if (btf_type_kflag(type)) { + if (btf_type_kflag(mtype)) { bitoffs += BTF_MEMBER_BIT_OFFSET(field->offset); ctx->last_bitsize = BTF_MEMBER_BITFIELD_SIZE(field->offset); } else {
--
2.53.0