fix(cpio): correct dev_t -> rmajor/rminor mapping

ddiss · johannbg · commit acc629abb0d7 · 2022-02-17T19:28:33.000Z
dev_t -> major/minor number mapping is more complicated than the incorrect major=(dev_t >> 8) minor=(dev_t & 0xff) mapping that we currently perform. Fix mapping to match Linux / glibc behaviour. Fixes: #1695 Reported-by: Ethan Wu <ethanwu10@gmail.com> Signed-off-by: David Disseldorp <ddiss@suse.de>
diff --git a/src/dracut-cpio/src/main.rs b/src/dracut-cpio/src/main.rs
@@ -361,9 +361,12 @@ fn archive_path<W: Seek + Write>(
         // no zero terminator for symlink target path
     }
 
+    // Linux kernel uses 32-bit dev_t, encoded as mmmM MMmm. glibc uses 64-bit
+    // MMMM Mmmm mmmM MMmm, which is compatible with the former.
     if ftype.is_block_device() || ftype.is_char_device() {
-        rmajor = (md.rdev() >> 8) as u32;
-        rminor = (md.rdev() & 0xff) as u32;
+        let rd = md.rdev();
+        rmajor = (((rd >> 32) & 0xfffff000) | ((rd >> 8) & 0x00000fff)) as u32;
+        rminor = (((rd >> 12) & 0xffffff00) | (rd & 0x000000ff)) as u32;
     }
 
     if ftype.is_file() {

Original file line number	Diff line number	Diff line change
`@@ -361,9 +361,12 @@ fn archive_path<W: Seek + Write>(`
`361`	`361`	`// no zero terminator for symlink target path`
`362`	`362`	`}`
`363`	`363`
	`364`	`+ // Linux kernel uses 32-bit dev_t, encoded as mmmM MMmm. glibc uses 64-bit`
	`365`	`+ // MMMM Mmmm mmmM MMmm, which is compatible with the former.`
`364`	`366`	`if ftype.is_block_device() \|\| ftype.is_char_device() {`
`365`		`- rmajor = (md.rdev() >> 8) as u32;`
`366`		`- rminor = (md.rdev() & 0xff) as u32;`
	`367`	`+ let rd = md.rdev();`
	`368`	`+ rmajor = (((rd >> 32) & 0xfffff000) \| ((rd >> 8) & 0x00000fff)) as u32;`
	`369`	`+ rminor = (((rd >> 12) & 0xffffff00) \| (rd & 0x000000ff)) as u32;`
`367`	`370`	`}`
`368`	`371`
`369`	`372`	`if ftype.is_file() {`