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os: Account for bytes to ignore when sharing input buffer 

When reading requests from the clients, the input buffer might be shared
and used between different clients.

If a given client sends a full request with non-zero bytes to ignore,
the bytes to ignore may still be non-zero even though the request is
full, in which case the buffer could be shared with another client who's
request will not be processed because of those bytes to ignore, leading
to a possible hang of the other client request.

To avoid the issue, make sure we have zero bytes to ignore left in the
input request when sharing the input buffer with another client.

CVE-2025-49178

This issue was discovered by Nils Emmerich <nemmerich@ernw.de> and
reported by Julian Suleder via ERNW Vulnerability Disclosure.

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/2024>
This commit is contained in:
Olivier Fourdan 2025-04-28 10:46:03 +02:00 committed by Enrico Weigelt
parent a1e44d3c4f
commit 0d6af5a542
1 changed files with 1 additions and 1 deletions
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2
os/io.c
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@ -442,7 +442,7 @@ ReadRequestFromClient(ClientPtr client)
*/
gotnow -= needed;
if (!gotnow)
if (!gotnow && !oci->ignoreBytes)
AvailableInput = oc;
if (move_header) {
if (client->req_len < bytes_to_int32(sizeof(xBigReq) - sizeof(xReq))) {