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io_uring/kbuf: hold io_buffer_list reference over mmap

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If we look up the kbuf, ensure that it doesn't get unregistered until
after we're done with it. Since we're inside mmap, we cannot safely use
the io_uring lock. Rely on the fact that we can lookup the buffer list
under RCU now and grab a reference to it, preventing it from being
unregistered until we're done with it. The lookup returns the
io_buffer_list directly with it referenced.

Cc: stable@vger.kernel.org # v6.4+
Fixes: 5cf4f52e6d ("io_uring: free io_buffer_list entries via RCU")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2024-04-02 16:16:03 -06:00
parent 6b69c4ab4f
commit 561e4f9451
3 changed files with 34 additions and 12 deletions
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11
io_uring/io_uring.c
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@ -3447,14 +3447,15 @@ static void *io_uring_validate_mmap_request(struct file *file,
ptr = ctx->sq_sqes; ptr = ctx->sq_sqes;
break; break;
case IORING_OFF_PBUF_RING: { case IORING_OFF_PBUF_RING: {
struct io_buffer_list *bl;
unsigned int bgid; unsigned int bgid;
bgid = (offset & ~IORING_OFF_MMAP_MASK) >> IORING_OFF_PBUF_SHIFT; bgid = (offset & ~IORING_OFF_MMAP_MASK) >> IORING_OFF_PBUF_SHIFT;
rcu_read_lock(); bl = io_pbuf_get_bl(ctx, bgid);
ptr = io_pbuf_get_address(ctx, bgid); if (IS_ERR(bl))
rcu_read_unlock(); return bl;
if (!ptr) ptr = bl->buf_ring;
return ERR_PTR(-EINVAL); io_put_bl(ctx, bl);
break; break;
} }
default: default:

31
io_uring/kbuf.c
View File

@ -266,7 +266,7 @@ static int __io_remove_buffers(struct io_ring_ctx *ctx,
return i; return i;
} }
static void io_put_bl(struct io_ring_ctx *ctx, struct io_buffer_list *bl) void io_put_bl(struct io_ring_ctx *ctx, struct io_buffer_list *bl)
{ {
if (atomic_dec_and_test(&bl->refs)) { if (atomic_dec_and_test(&bl->refs)) {
__io_remove_buffers(ctx, bl, -1U); __io_remove_buffers(ctx, bl, -1U);
@ -719,16 +719,35 @@ int io_register_pbuf_status(struct io_ring_ctx *ctx, void __user *arg)
return 0; return 0;
} }
void *io_pbuf_get_address(struct io_ring_ctx *ctx, unsigned long bgid) struct io_buffer_list *io_pbuf_get_bl(struct io_ring_ctx *ctx,
unsigned long bgid)
{ {
struct io_buffer_list *bl; struct io_buffer_list *bl;
bool ret;
bl = __io_buffer_get_list(ctx, bgid); /*
* We have to be a bit careful here - we're inside mmap and cannot grab
* the uring_lock. This means the buffer_list could be simultaneously
* going away, if someone is trying to be sneaky. Look it up under rcu
* so we know it's not going away, and attempt to grab a reference to
* it. If the ref is already zero, then fail the mapping. If successful,
* the caller will call io_put_bl() to drop the the reference at at the
* end. This may then safely free the buffer_list (and drop the pages)
* at that point, vm_insert_pages() would've already grabbed the
* necessary vma references.
*/
rcu_read_lock();
bl = xa_load(&ctx->io_bl_xa, bgid);
/* must be a mmap'able buffer ring and have pages */
ret = false;
if (bl && bl->is_mmap)
ret = atomic_inc_not_zero(&bl->refs);
rcu_read_unlock();
if (!bl || !bl->is_mmap) if (ret)
return NULL; return bl;
return bl->buf_ring; return ERR_PTR(-EINVAL);
} }
/* /*

4
io_uring/kbuf.h
View File

@ -61,7 +61,9 @@ void __io_put_kbuf(struct io_kiocb *req, unsigned issue_flags);
bool io_kbuf_recycle_legacy(struct io_kiocb *req, unsigned issue_flags); bool io_kbuf_recycle_legacy(struct io_kiocb *req, unsigned issue_flags);
void *io_pbuf_get_address(struct io_ring_ctx *ctx, unsigned long bgid); void io_put_bl(struct io_ring_ctx *ctx, struct io_buffer_list *bl);
struct io_buffer_list *io_pbuf_get_bl(struct io_ring_ctx *ctx,
unsigned long bgid);
static inline bool io_kbuf_recycle_ring(struct io_kiocb *req) static inline bool io_kbuf_recycle_ring(struct io_kiocb *req)
{ {