libbpf: Fix out-of-bound read

[ Upstream commit 236d3910117e9f97ebf75e511d8bcc950f1a4e5f ]

In `set_kcfg_value_str`, an untrusted string is accessed with the assumption
that it will be at least two characters long due to the presence of checks for
opening and closing quotes. But the check for the closing quote
(value[len - 1] != '"') misses the fact that it could be checking the opening
quote itself in case of an invalid input that consists of just the opening
quote.

This commit adds an explicit check to make sure the string is at least two
characters long.

Signed-off-by: Nandakumar Edamana <nandakumar@nandakumar.co.in>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250221210110.3182084-1-nandakumar@nandakumar.co.in
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 294fdba9c76f712d5f0e8dd4873116d5504a202f..40e0d84e3d8ed9e655577b54eef926378aa4a22d 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1567,7 +1567,7 @@ static int set_kcfg_value_str(struct extern_desc *ext, char *ext_val,
        }
 
        len = strlen(value);
-       if (value[len - 1] != '"') {
+       if (len < 2 || value[len - 1] != '"') {
                pr_warn("extern (kcfg) '%s': invalid string config '%s'\n",
                        ext->name, value);
                return -EINVAL;