[PATCH bpf] libbpf: handle unsupported mmap-based /sys/kernel/btf/vmlinux correctly

[PATCH bpf] libbpf: handle unsupported mmap-based /sys/kernel/btf/vmlinux correctly

[Andrii Nakryiko]

libbpf_err_ptr() helpers are meant to return NULL and set errno, if
there is an error. But btf_parse_raw_mmap() is meant to be used
internally and is expected to return ERR_PTR() values. Because of this
mismatch, when libbpf tries to mmap /sys/kernel/btf/vmlinux, we don't
detect the error correctly with IS_ERR() check, and never fallback to
old non-mmap-based way of loading vmlinux BTF.

Fix this by using proper ERR_PTR() returns internally.

Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Reviewed-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Fixes: 3c0421c93ce4 ("libbpf: Use mmap to parse vmlinux BTF from sysfs")
Cc: Lorenz Bauer <lmb@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/lib/bpf/btf.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index f1d495dc66bb..37682908cb0f 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -1384,12 +1384,12 @@ static struct btf *btf_parse_raw_mmap(const char *path, struct btf *base_btf)
 
 	fd = open(path, O_RDONLY);
 	if (fd < 0)
-		return libbpf_err_ptr(-errno);
+		return ERR_PTR(-errno);
 
 	if (fstat(fd, &st) < 0) {
 		err = -errno;
 		close(fd);
-		return libbpf_err_ptr(err);
+		return ERR_PTR(err);
 	}
 
 	data = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
@@ -1397,7 +1397,7 @@ static struct btf *btf_parse_raw_mmap(const char *path, struct btf *base_btf)
 	close(fd);
 
 	if (data == MAP_FAILED)
-		return libbpf_err_ptr(err);
+		return ERR_PTR(err);
 
 	btf = btf_new(data, st.st_size, base_btf, true);
 	if (IS_ERR(btf))
-- 
2.47.1

Re: [PATCH bpf] libbpf: handle unsupported mmap-based /sys/kernel/btf/vmlinux correctly

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Fri,  6 Jun 2025 13:21:34 -0700 you wrote:
> libbpf_err_ptr() helpers are meant to return NULL and set errno, if
> there is an error. But btf_parse_raw_mmap() is meant to be used
> internally and is expected to return ERR_PTR() values. Because of this
> mismatch, when libbpf tries to mmap /sys/kernel/btf/vmlinux, we don't
> detect the error correctly with IS_ERR() check, and never fallback to
> old non-mmap-based way of loading vmlinux BTF.
> 
> [...]

Here is the summary with links:
  - [bpf] libbpf: handle unsupported mmap-based /sys/kernel/btf/vmlinux correctly
    https://git.kernel.org/bpf/bpf/c/02670deede22

You are awesome, thank you!
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