[PATCH bpf 2/2] libbpf: fix possible use after free in xsk_socket__delete

[Magnus Karlsson]

From: Magnus Karlsson <magnus.karls...@intel.com>

Fix a possible use after free in xsk_socket__delete that will happen
if xsk_put_ctx() frees the ctx. To fix, save the umem reference taken
from the context and just use that instead.

Fixes: 2f6324a3937f ("libbpf: Support shared umems between queues and devices")
Signed-off-by: Magnus Karlsson <magnus.karls...@intel.com>
---
 tools/lib/bpf/xsk.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index 504b7a8..9bc537d 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -892,6 +892,7 @@ void xsk_socket__delete(struct xsk_socket *xsk)
 {
        size_t desc_sz = sizeof(struct xdp_desc);
        struct xdp_mmap_offsets off;
+       struct xsk_umem *umem;
        struct xsk_ctx *ctx;
        int err;
 
@@ -899,6 +900,7 @@ void xsk_socket__delete(struct xsk_socket *xsk)
                return;
 
        ctx = xsk->ctx;
+       umem = ctx->umem;
        if (ctx->prog_fd != -1) {
                xsk_delete_bpf_maps(xsk);
                close(ctx->prog_fd);
@@ -918,11 +920,11 @@ void xsk_socket__delete(struct xsk_socket *xsk)
 
        xsk_put_ctx(ctx);
 
-       ctx->umem->refcount--;
+       umem->refcount--;
        /* Do not close an fd that also has an associated umem connected
         * to it.
         */
-       if (xsk->fd != ctx->umem->fd)
+       if (xsk->fd != umem->fd)
                close(xsk->fd);
        free(xsk);
 }
-- 
2.7.4