This is a note to let you know that I've just added the patch titled
lib/decompress_unlz4.c: correctly handle zero-padding around initrds.
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
lib-decompress_unlz4.c-correctly-handle-zero-padding.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit a6dc922a2baf3dfd87703f440df543e28b57fa0a
Author: Dimitri John Ledkov <dimitri.ledkov@xxxxxxxxxxxxx>
Date: Wed Jun 30 18:56:16 2021 -0700
lib/decompress_unlz4.c: correctly handle zero-padding around initrds.
[ Upstream commit 2c484419efc09e7234c667aa72698cb79ba8d8ed ]
lz4 compatible decompressor is simple. The format is underspecified and
relies on EOF notification to determine when to stop. Initramfs buffer
format[1] explicitly states that it can have arbitrary number of zero
padding. Thus when operating without a fill function, be extra careful to
ensure that sizes less than 4, or apperantly empty chunksizes are treated
as EOF.
To test this I have created two cpio initrds, first a normal one,
main.cpio. And second one with just a single /test-file with content
"second" second.cpio. Then i compressed both of them with gzip, and with
lz4 -l. Then I created a padding of 4 bytes (dd if=/dev/zero of=pad4 bs=1
count=4). To create four testcase initrds:
1) main.cpio.gzip + extra.cpio.gzip = pad0.gzip
2) main.cpio.lz4 + extra.cpio.lz4 = pad0.lz4
3) main.cpio.gzip + pad4 + extra.cpio.gzip = pad4.gzip
4) main.cpio.lz4 + pad4 + extra.cpio.lz4 = pad4.lz4
The pad4 test-cases replicate the initrd load by grub, as it pads and
aligns every initrd it loads.
All of the above boot, however /test-file was not accessible in the initrd
for the testcase #4, as decoding in lz4 decompressor failed. Also an
error message printed which usually is harmless.
Whith a patched kernel, all of the above testcases now pass, and
/test-file is accessible.
This fixes lz4 initrd decompress warning on every boot with grub. And
more importantly this fixes inability to load multiple lz4 compressed
initrds with grub. This patch has been shipping in Ubuntu kernels since
January 2021.
[1] ./Documentation/driver-api/early-userspace/buffer-format.rst
BugLink: https://bugs.launchpad.net/bugs/1835660
Link: https://lore.kernel.org/lkml/20210114200256.196589-1-xnox@xxxxxxxxxx/ # v0
Link: https://lkml.kernel.org/r/20210513104831.432975-1-dimitri.ledkov@xxxxxxxxxxxxx
Signed-off-by: Dimitri John Ledkov <dimitri.ledkov@xxxxxxxxxxxxx>
Cc: Kyungsik Lee <kyungsik.lee@xxxxxxx>
Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
Cc: Bongkyu Kim <bongkyu.kim@xxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Sven Schmidt <4sschmid@xxxxxxxxxxxxxxxxxxxxxxxxx>
Cc: Rajat Asthana <thisisrast7@xxxxxxxxx>
Cc: Nick Terrell <terrelln@xxxxxx>
Cc: Gao Xiang <hsiangkao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/lib/decompress_unlz4.c b/lib/decompress_unlz4.c
index c0cfcfd486be..e6327391b6b6 100644
--- a/lib/decompress_unlz4.c
+++ b/lib/decompress_unlz4.c
@@ -112,6 +112,9 @@ STATIC inline int INIT unlz4(u8 *input, long in_len,
error("data corrupted");
goto exit_2;
}
+ } else if (size < 4) {
+ /* empty or end-of-file */
+ goto exit_3;
}
chunksize = get_unaligned_le32(inp);
@@ -125,6 +128,10 @@ STATIC inline int INIT unlz4(u8 *input, long in_len,
continue;
}
+ if (!fill && chunksize == 0) {
+ /* empty or end-of-file */
+ goto exit_3;
+ }
if (posp)
*posp += 4;
@@ -184,6 +191,7 @@ STATIC inline int INIT unlz4(u8 *input, long in_len,
}
}
+exit_3:
ret = 0;
exit_2:
if (!input)
