[PATCH 5.15 534/691] tomoyo: fallback to realpath if symlinks pathname does not exist

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5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>

commit ada1986d07976d60bed5017aa38b7f7cf27883f7 upstream.

Alfred Agrell found that TOMOYO cannot handle execveat(AT_EMPTY_PATH)
inside chroot environment where /dev and /proc are not mounted, for
commit 51f39a1f0cea ("syscalls: implement execveat() system call") missed
that TOMOYO tries to canonicalize argv[0] when the filename fed to the
executed program as argv[0] is supplied using potentially nonexistent
pathname.

Since "/dev/fd/<fd>" already lost symlink information used for obtaining
that <fd>, it is too late to reconstruct symlink's pathname. Although
<filename> part of "/dev/fd/<fd>/<filename>" might not be canonicalized,
TOMOYO cannot use tomoyo_realpath_nofollow() when /dev or /proc is not
mounted. Therefore, fallback to tomoyo_realpath_from_path() when
tomoyo_realpath_nofollow() failed.

Reported-by: Alfred Agrell <blubban@xxxxxxxxx>
Closes: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1082001
Fixes: 51f39a1f0cea ("syscalls: implement execveat() system call")
Cc: stable@xxxxxxxxxxxxxxx # v3.19+
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 security/tomoyo/domain.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/security/tomoyo/domain.c
+++ b/security/tomoyo/domain.c
@@ -723,10 +723,13 @@ int tomoyo_find_next_domain(struct linux
 	ee->r.obj = &ee->obj;
 	ee->obj.path1 = bprm->file->f_path;
 	/* Get symlink's pathname of program. */
-	retval = -ENOENT;
 	exename.name = tomoyo_realpath_nofollow(original_name);
-	if (!exename.name)
-		goto out;
+	if (!exename.name) {
+		/* Fallback to realpath if symlink's pathname does not exist. */
+		exename.name = tomoyo_realpath_from_path(&bprm->file->f_path);
+		if (!exename.name)
+			goto out;
+	}
 	tomoyo_fill_path_info(&exename);
 retry:
 	/* Check 'aggregator' directive. */






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