[PATCH 1/2] libkmod-file: gracefully handle errors from zlib

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zlib won't necessarily set the system errno, and this is particularly
evident on corrupted data (which results in a double free). Use zlib's
gzerror to detect the failure, returning a generic EINVAL when zlib
doesn't provide us with an errno.
---
This fixes a crash that I had seen a few times from Arch users, but was never
able to pin down, with the reporter disappearing fairly quickly. I finally
traced it to corrupted gzip archives, which kmod should definitely not be
exploding on, no matter how invalid they are. Below is a link to one such
corrupted module to replicate the bug:

http://dev.archlinux.org/~dreisner/hid-sunplus.ko.gz

 libkmod/libkmod-file.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/libkmod/libkmod-file.c b/libkmod/libkmod-file.c
index 46ad8d9..8beb7e3 100644
--- a/libkmod/libkmod-file.c
+++ b/libkmod/libkmod-file.c
@@ -199,7 +199,13 @@ static int load_zlib(struct kmod_file *file)
 		if (r == 0)
 			break;
 		else if (r < 0) {
-			err = -errno;
+			int gzerr;
+			const char *gz_errmsg = gzerror(file->gzf, &gzerr);
+
+			ERR(file->ctx, "gzip: %s\n", gz_errmsg);
+
+			/* gzip might not set errno here */
+			err = gzerr == Z_ERRNO ? -errno : -EINVAL;
 			goto error;
 		}
 		did += r;
-- 
1.7.10.1

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