Merge patch series "binfmt: fixes for kres reports"

Christian Brauner <brauner@kernel.org> says:

I asked Chris to run his kres tooling on the binfmt with bpf changes
merged for this cycle. It found two issues that are fixed in this
series. I reproduced both of them.

* patches from https://patch.msgid.link/20260918-work-binfmt_misc-fixes-v1-0-647b24bc1c46@kernel.org:
  binfmt_misc: fix racy checks in bpf set_interp kfuncs
  binfmt_misc: fix OOB read in bpf_binprm_select_interp()

Link: https://patch.msgid.link/20260918-work-binfmt_misc-fixes-v1-0-647b24bc1c46@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

1 files changed, 32 insertions, 3 deletions

diff --git a/fs/binfmt_misc_bpf.c b/fs/binfmt_misc_bpf.c
index 91576ff05911..a3e26e8a4027 100644
--- a/fs/binfmt_misc_bpf.c
+++ b/fs/binfmt_misc_bpf.c
@@ -141,8 +141,6 @@ __bpf_kfunc int bpf_binprm_set_interp(struct linux_binprm *bprm,
 	len = strnlen(path, path__sz);
 	if (len == path__sz)
 		return -EINVAL;
-	if (path[0] != '/')
-		return -EINVAL;
 	if (len >= PATH_MAX)
 		return -ENAMETOOLONG;
 
@@ -150,6 +148,15 @@ __bpf_kfunc int bpf_binprm_set_interp(struct linux_binprm *bprm,
 	if (!interp)
 		return -ENOMEM;
 
+	/*
+	 * The program may pass memory that is written to while this runs,
+	 * so check the private copy and not the buffer it was made from.
+	 */
+	if (interp[0] != '/') {
+		kfree(interp);
+		return -EINVAL;
+	}
+
 	bm_bpf_stage_selection(bprm, interp, NULL);
 	return 0;
 }
@@ -176,6 +183,7 @@ __bpf_kfunc int bpf_binprm_select_interp(struct linux_binprm *bprm,
 					 const char *name, size_t name__sz)
 {
 	const struct binfmt_misc_interp *interp;
+	char buf[BINFMT_MISC_INTERP_NAME_MAX + 1];
 	size_t len;
 	char *path;
 
@@ -184,8 +192,20 @@ __bpf_kfunc int bpf_binprm_select_interp(struct linux_binprm *bprm,
 	len = strnlen(name, name__sz);
 	if (len == name__sz || !len)
 		return -EINVAL;
+	/* No entry binds a longer name, so it cannot be found. */
+	if (len > BINFMT_MISC_INTERP_NAME_MAX)
+		return -ENOENT;
+
+	/*
+	 * The program may pass memory that is written to while this runs,
+	 * so look the name up in a private copy and check that instead.
+	 */
+	memcpy(buf, name, len);
+	buf[len] = '\0';
+	if (!buf[0])
+		return -EINVAL;
 
-	interp = binfmt_misc_find_interp(bprm->bpf_interps, name);
+	interp = binfmt_misc_find_interp(bprm->bpf_interps, buf);
 	if (!interp)
 		return -ENOENT;
 
@@ -228,6 +248,15 @@ __bpf_kfunc int bpf_binprm_set_interp_arg(struct linux_binprm *bprm,
 	if (!val)
 		return -ENOMEM;
 
+	/*
+	 * The program may pass memory that is written to while this runs,
+	 * so check the private copy and not the buffer it was made from.
+	 */
+	if (!val[0]) {
+		kfree(val);
+		return -EINVAL;
+	}
+
 	kfree(bprm->bpf_interp_arg);
 	bprm->bpf_interp_arg = val;
 	return 0;