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 194809da51725ea8149faa325abf665f0aa47610..1cc87dbd015d80224e82e070000c963fd659eb82 100644 (file)
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2106,7 +2106,7 @@ 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;