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Peter Anvin" , Sasha Levin Subject: [PATCH 6.18 537/869] lib: decompress_bunzip2: fix integer overflow in run-length decoding Date: Sat, 7 Nov 2026 08:53:39 -0500 Message-ID: <20261107134911.644007068@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261107134852.069646174@linuxfoundation.org> References: <20261107134852.069646174@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Aamir Ahmed [ Upstream commit b822ad8d702df0be9fe3f24f71caeb0522d72319 ] 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: Signed-off-by: Sasha Levin --- lib/decompress_bunzip2.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/lib/decompress_bunzip2.c b/lib/decompress_bunzip2.c index 4f98cdea7e0b3..b8fb40ed06d22 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; } -- 2.53.0