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 33cdcfe10634488ddf6d96816dc6df182751d400..f65e03e7cf94461a1cbed1caef04e1ca3a959ca5 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1503,7 +1503,7 @@ 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;