queue-6.19/bpf-add-a-map-btf-from-a-fd-array-more-consistently.patch

From a2ab6fb298c00d45b603cec8621670515963fafe Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Fri, 13 Feb 2026 21:29:49 +0000
Subject: bpf: Add a map/btf from a fd array more consistently

From: Anton Protopopov <a.s.protopopov@gmail.com>

[ Upstream commit b0b1a8583d8e797114e613139e3e3318a1704690 ]

The add_fd_from_fd_array() function takes a file descriptor as a
parameter and tries to add either map or btf to the corresponding
list of used objects. As was reported by Dan Carpenter, since the
commit c81e4322acf0 ("bpf: Fix a potential use-after-free of BTF
object"), the fdget() is called twice on the file descriptor, and
thus userspace, potentially, can replace the file pointed to by the
file descriptor in between the two calls. On practice, this shouldn't
break anything on the kernel side, but for consistency fix the code
such that only one fdget() is executed.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/aY689z7gHNv8rgVO@stanley.mountain/
Fixes: ccd2d799ed44 ("bpf: Fix a potential use-after-free of BTF object")
Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
Link: https://lore.kernel.org/r/20260213212949.759321-1-a.s.protopopov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/bpf/verifier.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a16aca34f5834..fe01edfcc34c6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -24658,9 +24658,11 @@ static int add_fd_from_fd_array(struct bpf_verifier_env *env, int fd)
 		return 0;
 	}
 
-	btf = btf_get_by_fd(fd);
-	if (!IS_ERR(btf))
+	btf = __btf_get_by_fd(f);
+	if (!IS_ERR(btf)) {
+		btf_get(btf);
 		return __add_used_btf(env, btf);
+	}
 
 	verbose(env, "fd %d is not pointing to valid bpf_map or btf\n", fd);
 	return PTR_ERR(map);
-- 
2.51.0