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List:       kernel-hardening
Subject:    [PATCH v7 1/7] exec: Change uselib(2) IS_SREG() failure to EACCES
From:       Mickaël Salaün <mic () digikod ! net>
Date:       2020-07-23 17:12:21
Message-ID: 20200723171227.446711-2-mic () digikod ! net
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From: Kees Cook <keescook@chromium.org>

Change uselib(2)' S_ISREG() error return to EACCES instead of EINVAL so
the behavior matches execve(2), and the seemingly documented value.
The "not a regular file" failure mode of execve(2) is explicitly
documented[1], but it is not mentioned in uselib(2)[2] which does,
however, say that open(2) and mmap(2) errors may apply. The documentation
for open(2) does not include a "not a regular file" error[3], but mmap(2)
does[4], and it is EACCES.

[1] http://man7.org/linux/man-pages/man2/execve.2.html#ERRORS
[2] http://man7.org/linux/man-pages/man2/uselib.2.html#ERRORS
[3] http://man7.org/linux/man-pages/man2/open.2.html#ERRORS
[4] http://man7.org/linux/man-pages/man2/mmap.2.html#ERRORS

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/r/20200605160013.3954297-2-keescook@chromium.org
---
 fs/exec.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index e6e8a9a70327..d7c937044d10 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -141,11 +141,10 @@ SYSCALL_DEFINE1(uselib, const char __user *, library)
 	if (IS_ERR(file))
 		goto out;
 
-	error = -EINVAL;
+	error = -EACCES;
 	if (!S_ISREG(file_inode(file)->i_mode))
 		goto exit;
 
-	error = -EACCES;
 	if (path_noexec(&file->f_path))
 		goto exit;
 
-- 
2.27.0

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