[PATCH v2] erofs-utils: tar: handle gzread errors

[Gao Xiang <hsiangkao@linux.alibaba.com>]

From: Vansh Choudhary <ch@vnsh.in>

Treat gzread() errors as I/O failures before updating the stream
buffer state.

Without that, a negative gzread() result could underflow ios->tail
and leave the reader in a corrupted state.

Signed-off-by: Vansh Choudhary <ch@vnsh.in>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
---
v2:
 - some cleanups.

I will apply this one.

 lib/tar.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/lib/tar.c b/lib/tar.c
index eca29f54c06f..0fe9853dfb16 100644
--- a/lib/tar.c
+++ b/lib/tar.c
@@ -170,16 +170,17 @@ int erofs_iostream_read(struct erofs_iostream *ios, void **buf, u64 bytes)
 #if defined(HAVE_ZLIB)
 			ret = gzread(ios->handler, ios->buffer + rabytes,
 				     ios->bufsize - rabytes);
-			if (!ret) {
-				int errnum;
+			if (ret <= 0) {
 				const char *errstr;
+				int errnum;
 
 				errstr = gzerror(ios->handler, &errnum);
-				if (errnum != Z_STREAM_END) {
+				if (!ret && errnum == Z_STREAM_END) {
+					ios->feof = true;
+				} else {
 					erofs_err("failed to gzread: %s", errstr);
 					return -EIO;
 				}
-				ios->feof = true;
 			}
 			ios->tail += ret;
 #else
-- 
2.43.5