makedevs: resync device creation with upstream busybox

We use makedevs to create device nodes in the target rootfs. However, this can be called several times, e.g. when building several filesystem images or when rebuilding. When makedevs is called the second time, the device node already exists so mknod() errors out.

This wasn't noticed before because fakeroot's mknod() wrapper (incorrectly) does _not_ error out when the file exists already. Now we switched from fakeroot to pseudo, the problem becomes apparent.

Before creating the device node, check if it already exists and if so, if it has the correct device type and number. Change of mode and ownership is still done.

This approach was preferred over removing the target files before creating them, which would be simpler. However, when e.g. a file exists as a normal file and makedevs specifies it as a device node, that really is an error so we should detect it.

The other types don't have to be changed. The 'd' (directory) type is already OK because it already only creates directories if they don't exist yet. The 'f' (file mode) and 'r' (recursive) types only operate on files and directories that exist already.

Patch also sent upstream to busybox.

Signed-off-by Arnout Vandecappelle (Essensium/Mind) <[email protected]>

Reported-by Fabio Estevam <[email protected]>

We use makedevs to create device nodes in the target rootfs. However, this can be called several times, e.g. when building several filesystem images or when rebuilding. When makedevs is called the second time, the device node already exists so mknod() errors out.

This wasn't noticed before because fakeroot's mknod() wrapper (incorrectly) does _not_ error out when the file exists already. Now we switched from fakeroot to pseudo, the problem becomes apparent.

Before creating the device node, check if it already exists and if so, if it has the correct device type and number. Change of mode and ownership is still done.

This approach was preferred over removing the target files before creating them, which would be simpler. However, when e.g. a file exists as a normal file and makedevs specifies it as a device node, that really is an error so we should detect it.

The other types don't have to be changed. The 'd' (directory) type is already OK because it already only creates directories if they don't exist yet. The 'f' (file mode) and 'r' (recursive) types only operate on files and directories that exist already.

Patch also sent upstream to busybox.

Signed-off-by Arnout Vandecappelle (Essensium/Mind) <[email protected]>

Reported-by Fabio Estevam <[email protected]>

---
v2: check if pre-existing file is of correct type instead of simply
unlinking (Yann).

---
 package/makedevs/makedevs.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

package/makedevs/makedevs.c +16 -2

index 7092b14..bcf0e0f 100644
@@ -601,6 +601,7 @@ int main(int argc, char **argv)
 			dev_t rdev;
 			unsigned i;
 			char *full_name_inc;
+			struct stat st;
 
 			if (type == 'p') {
 				mode |= S_IFIFO;

@@ -622,10 +623,23 @@ int main(int argc, char **argv)
 			for (i = start; i <= start + count; i++) {
 				sprintf(full_name_inc, count ? "%s%u" : "%s", full_name, i);
 				rdev = makedev(major, minor + (i - start) * increment);
-				if (mknod(full_name_inc, mode, rdev) < 0) {
+				if (stat(full_name_inc, &st) == 0) {
+					if ((mode & S_IFMT) != (st.st_mode & S_IFMT)) {
+						bb_error_msg("line %d: node %s exists but is of wrong file type", linenum, full_name_inc);
+						ret = EXIT_FAILURE;
+						continue;
+					}
+					if (st.st_rdev != rdev) {
+						bb_error_msg("line %d: node %s exists but is wrong device number", linenum, full_name_inc);
+						ret = EXIT_FAILURE;
+						continue;
+					}
+				} else if (mknod(full_name_inc, mode, rdev) < 0) {
 					bb_perror_msg("line %d: can't create node %s", linenum, full_name_inc);
 					ret = EXIT_FAILURE;
-				} else if (chown(full_name_inc, uid, gid) < 0) {
+					continue;
+				}
+				if (chown(full_name_inc, uid, gid) < 0) {
 					bb_perror_msg("line %d: can't chown %s", linenum, full_name_inc);
 					ret = EXIT_FAILURE;
 				} else if (chmod(full_name_inc, mode) < 0) {

Signature · 6 lines

2.9.3

_______________________________________________
buildroot mailing list
buildroot at busybox.net
http://lists.busybox.net/mailman/listinfo/buildroot

In upstream busbyox, the code to create devices has been simplified:
the code for a single and for multiple devices is no longer duplicated.

Since we are going to change the device creation code next, it's convenient to have only one copy to modify.

There are two behavioural changes with this, but they were introduced silently together with other commits in upstream busybox.

- When mknod() fails, the chmod was still done. This is pointless so it is no longer done now.

- There was a check for mode != -1; however, a mode of -1 would not have worked anyway because all bits would be set for mknod(), which would fail. So this check is redundant.

Signed-off-by Arnout Vandecappelle (Essensium/Mind) <[email protected]>

In upstream busbyox, the code to create devices has been simplified:
the code for a single and for multiple devices is no longer duplicated.

Since we are going to change the device creation code next, it's convenient to have only one copy to modify.

There are two behavioural changes with this, but they were introduced silently together with other commits in upstream busybox.

- When mknod() fails, the chmod was still done. This is pointless so it is no longer done now.

- There was a check for mode != -1; however, a mode of -1 would not have worked anyway because all bits would be set for mknod(), which would fail. So this check is redundant.

Signed-off-by Arnout Vandecappelle (Essensium/Mind) <[email protected]>

---
 package/makedevs/makedevs.c | 47 +++++++++++++++------------------------------
 1 file changed, 15 insertions(+), 32 deletions(-)

package/makedevs/makedevs.c +15 -32

index cacb144..7092b14 100644
@@ -599,6 +599,8 @@ int main(int argc, char **argv)
 		} else
 		{
 			dev_t rdev;
+			unsigned i;
+			char *full_name_inc;
 
 			if (type == 'p') {
 				mode |= S_IFIFO;

@@ -614,43 +616,24 @@ int main(int argc, char **argv)
 				goto loop;
 			}
 
-			if (count > 0) {
-				int i;
-				char *full_name_inc;
-
-				full_name_inc = xmalloc(strlen(full_name) + 8);
-				for (i = 0; i < count; i++) {
-					sprintf(full_name_inc, "%s%d", full_name, start + i);
-					rdev = makedev(major, minor + i * increment);
-					if (mknod(full_name_inc, mode, rdev) == -1) {
-						bb_perror_msg("line %d: Couldnt create node %s", linenum, full_name_inc);
-						ret = EXIT_FAILURE;
-					}
-					else if (chown(full_name_inc, uid, gid) == -1) {
-						bb_perror_msg("line %d: chown failed for %s", linenum, full_name_inc);
-						ret = EXIT_FAILURE;
-					}
-					if ((mode != -1) && (chmod(full_name_inc, mode) < 0)){
-						bb_perror_msg("line %d: chmod failed for %s", linenum, full_name_inc);
-						ret = EXIT_FAILURE;
-					}
-				}
-				free(full_name_inc);
-			} else {
-				rdev = makedev(major, minor);
-				if (mknod(full_name, mode, rdev) == -1) {
-					bb_perror_msg("line %d: Couldnt create node %s", linenum, full_name);
+			full_name_inc = xmalloc(strlen(full_name) + sizeof(int)*3 + 2);
+			if (count)
+				count--;
+			for (i = start; i <= start + count; i++) {
+				sprintf(full_name_inc, count ? "%s%u" : "%s", full_name, i);
+				rdev = makedev(major, minor + (i - start) * increment);
+				if (mknod(full_name_inc, mode, rdev) < 0) {
+					bb_perror_msg("line %d: can't create node %s", linenum, full_name_inc);
 					ret = EXIT_FAILURE;
-				}
-				else if (chown(full_name, uid, gid) == -1) {
-					bb_perror_msg("line %d: chown failed for %s", linenum, full_name);
+				} else if (chown(full_name_inc, uid, gid) < 0) {
+					bb_perror_msg("line %d: can't chown %s", linenum, full_name_inc);
 					ret = EXIT_FAILURE;
-				}
-				if ((mode != -1) && (chmod(full_name, mode) < 0)){
-					bb_perror_msg("line %d: chmod failed for %s", linenum, full_name);
+				} else if (chmod(full_name_inc, mode) < 0) {
+					bb_perror_msg("line %d: can't chmod %s", linenum, full_name_inc);
 					ret = EXIT_FAILURE;
 				}
 			}
+			free(full_name_inc);
 		}
 loop:
 		free(line);

Signature · 6 lines

2.9.3

_______________________________________________
buildroot mailing list
buildroot at busybox.net
http://lists.busybox.net/mailman/listinfo/buildroot

In upstream busbyox, the code to create devices has been simplified:
the code for a single and for multiple devices is no longer duplicated.

Since we are going to change the device creation code next, it's convenient to have only one copy to modify.

There are two behavioural changes with this, but they were introduced silently together with other commits in upstream busybox.

- When mknod() fails, the chmod was still done. This is pointless so it is no longer done now.

- There was a check for mode != -1; however, a mode of -1 would not have worked anyway because all bits would be set for mknod(), which would fail. So this check is redundant.

Signed-off-by Arnout Vandecappelle (Essensium/Mind) <[email protected]>

---
 package/makedevs/makedevs.c | 47 +++++++++++++++------------------------------
 1 file changed, 15 insertions(+), 32 deletions(-)