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authorKees Cook <keescook@chromium.org>2020-08-11 18:36:26 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-12 10:58:01 -0700
commit633fb6ac39801514613fbe050db6abdc3fe744d5 (patch)
treeb2a4509122ee07078297aa873319c1e2473de379 /fs
parentdb19c91c3b75cf8ece3ffd92a4e84a306a7547b0 (diff)
exec: move S_ISREG() check earlier
The execve(2)/uselib(2) syscalls have always rejected non-regular files. Recently, it was noticed that a deadlock was introduced when trying to execute pipes, as the S_ISREG() test was happening too late. This was fixed in commit 73601ea5b7b1 ("fs/open.c: allow opening only regular files during execve()"), but it was added after inode_permission() had already run, which meant LSMs could see bogus attempts to execute non-regular files. Move the test into the other inode type checks (which already look for other pathological conditions[1]). Since there is no need to use FMODE_EXEC while we still have access to "acc_mode", also switch the test to MAY_EXEC. Also include a comment with the redundant S_ISREG() checks at the end of execve(2)/uselib(2) to note that they are present to avoid any mistakes. My notes on the call path, and related arguments, checks, etc: do_open_execat() struct open_flags open_exec_flags = { .open_flag = O_LARGEFILE | O_RDONLY | __FMODE_EXEC, .acc_mode = MAY_EXEC, ... do_filp_open(dfd, filename, open_flags) path_openat(nameidata, open_flags, flags) file = alloc_empty_file(open_flags, current_cred()); do_open(nameidata, file, open_flags) may_open(path, acc_mode, open_flag) /* new location of MAY_EXEC vs S_ISREG() test */ inode_permission(inode, MAY_OPEN | acc_mode) security_inode_permission(inode, acc_mode) vfs_open(path, file) do_dentry_open(file, path->dentry->d_inode, open) /* old location of FMODE_EXEC vs S_ISREG() test */ security_file_open(f) open() [1] https://lore.kernel.org/lkml/202006041910.9EF0C602@keescook/ Signed-off-by: Kees Cook <keescook@chromium.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Aleksa Sarai <cyphar@cyphar.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Christian Brauner <christian.brauner@ubuntu.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Eric Biggers <ebiggers3@gmail.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Link: http://lkml.kernel.org/r/20200605160013.3954297-3-keescook@chromium.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/exec.c14
-rw-r--r--fs/namei.c6
-rw-r--r--fs/open.c6
3 files changed, 16 insertions, 10 deletions
diff --git a/fs/exec.c b/fs/exec.c
index c56aad307069..cc7ec7b9000b 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -141,8 +141,13 @@ SYSCALL_DEFINE1(uselib, const char __user *, library)
if (IS_ERR(file))
goto out;
+ /*
+ * may_open() has already checked for this, so it should be
+ * impossible to trip now. But we need to be extra cautious
+ * and check again at the very end too.
+ */
error = -EACCES;
- if (!S_ISREG(file_inode(file)->i_mode))
+ if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode)))
goto exit;
if (path_noexec(&file->f_path))
@@ -908,8 +913,13 @@ static struct file *do_open_execat(int fd, struct filename *name, int flags)
if (IS_ERR(file))
goto out;
+ /*
+ * may_open() has already checked for this, so it should be
+ * impossible to trip now. But we need to be extra cautious
+ * and check again at the very end too.
+ */
err = -EACCES;
- if (!S_ISREG(file_inode(file)->i_mode))
+ if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode)))
goto exit;
if (path_noexec(&file->f_path))
diff --git a/fs/namei.c b/fs/namei.c
index fde8fe086c09..9cc3b90abdff 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2849,16 +2849,18 @@ static int may_open(const struct path *path, int acc_mode, int flag)
case S_IFLNK:
return -ELOOP;
case S_IFDIR:
- if (acc_mode & MAY_WRITE)
+ if (acc_mode & (MAY_WRITE | MAY_EXEC))
return -EISDIR;
break;
case S_IFBLK:
case S_IFCHR:
if (!may_open_dev(path))
return -EACCES;
- /*FALLTHRU*/
+ fallthrough;
case S_IFIFO:
case S_IFSOCK:
+ if (acc_mode & MAY_EXEC)
+ return -EACCES;
flag &= ~O_TRUNC;
break;
}
diff --git a/fs/open.c b/fs/open.c
index c80e9f497e9b..9af548fb841b 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -779,12 +779,6 @@ static int do_dentry_open(struct file *f,
return 0;
}
- /* Any file opened for execve()/uselib() has to be a regular file. */
- if (unlikely(f->f_flags & FMODE_EXEC && !S_ISREG(inode->i_mode))) {
- error = -EACCES;
- goto cleanup_file;
- }
-
if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
error = get_write_access(inode);
if (unlikely(error))