From: Dimitri John Ledkov dimitri.ledkov@canonical.com
[ 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@ubuntu.com/ # v0 Link: https://lkml.kernel.org/r/20210513104831.432975-1-dimitri.ledkov@canonical.c... Signed-off-by: Dimitri John Ledkov dimitri.ledkov@canonical.com Cc: Kyungsik Lee kyungsik.lee@lge.com Cc: Yinghai Lu yinghai@kernel.org Cc: Bongkyu Kim bongkyu.kim@lge.com Cc: Kees Cook keescook@chromium.org Cc: Sven Schmidt 4sschmid@informatik.uni-hamburg.de Cc: Rajat Asthana thisisrast7@gmail.com Cc: Nick Terrell terrelln@fb.com Cc: Gao Xiang hsiangkao@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- lib/decompress_unlz4.c | 8 ++++++++ 1 file changed, 8 insertions(+)
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)