From b822ad8d702df0be9fe3f24f71caeb0522d72319 Mon Sep 17 00:00:00 2001 From: Aamir Ahmed Date: Wed, 16 Sep 2026 09:53:51 +0100 Subject: [PATCH] lib: decompress_bunzip2: fix integer overflow in run-length decoding The RUNA/RUNB decoder in get_next_block() accumulates a run length into the signed int t with no bound. runPos doubles per symbol, so t grows as at least 2^n-1 and reaches INT_MAX after 31 RUNA symbols. The guard that follows, dbufCount+t >= dbufSize, is itself a signed addition, and as the kernel builds with -fno-strict-overflow it wraps negative once dbufCount is nonzero, so the guard is skipped. while (t--) dbuf[dbufCount++] = uc then writes INT_MAX entries into a buffer holding at most 900000. One literal symbol ahead of the run is enough to make dbufCount nonzero. Bound t to the block size as it is accumulated. t only grows within a run, so the value tested never exceeds the final run length; any stream that decodes today satisfies dbufCount+t < dbufSize at the flush, hence t < dbufSize throughout, and no such stream is rejected. Because t grows as at least 2^n-1 the bound trips by the 20th symbol, leaving runPos at most 2^19, so the following runPos <<= 1 cannot overflow either. Link: https://lore.kernel.org/AS8P251MB00010FE5E38D253CF98A652AC8B92@AS8P251MB0001.EURP251.PROD.OUTLOOK.COM Fixes: bc22c17e12c1 ("bzip2/lzma: library support for gzip, bzip2 and lzma decompression") Signed-off-by: Aamir Ahmed Signed-off-by: Andrew Morton Assisted-by: LLM Cc: Alain Knaff Cc: "H. Peter Anvin" Cc: --- lib/decompress_bunzip2.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/lib/decompress_bunzip2.c b/lib/decompress_bunzip2.c index aaa75404250e..a9236d3e9678 100644 --- a/lib/decompress_bunzip2.c +++ b/lib/decompress_bunzip2.c @@ -428,6 +428,10 @@ static int INIT get_next_block(struct bunzip_data *bd) t += (runPos << nextSym); /* +runPos if RUNA; +2*runPos if RUNB */ + /* Bound the run so t and runPos cannot overflow. */ + if (t >= dbufSize) + return RETVAL_DATA_ERROR; + runPos <<= 1; continue; }