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Date: Fri, 24 May 2024 01:46:19 +0900
From: asmadeus@...ewreck.org
To: David Howells <dhowells@...hat.com>
Cc: syzbot <syzbot+d7c7a495a5e466c031b6@...kaller.appspotmail.com>,
brauner@...nel.org, hdanton@...a.com, linux-kernel@...r.kernel.org,
syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [v9fs?] KASAN: slab-use-after-free Read in
p9_fid_destroy
David Howells wrote on Thu, May 23, 2024 at 03:37:38PM +0100:
> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
>
> netfs, 9p: Fix race between umount and async request completion [v2]
>
> There's a problem in 9p's interaction with netfslib whereby a crash occurs
> because the 9p_fid structs get forcibly destroyed during client teardown
> (without paying attention to their refcounts) before netfslib has finished
> with them. However, it's not a simple case of deferring the clunking that
> p9_fid_put() does as that requires the client.
"as that requires the client" doesn't parse
> The problem is that netfslib has to unlock pages and clear the IN_PROGRESS
> flag before destroying the objects involved - including the pid - and, in
s/pid/fid/
> any case, nothing checks to see if writeback completed barring looking at
> the page flags.
>
> Fix this by keeping a count of outstanding I/O requests (of any type) and
> waiting for it to quiesce during inode eviction.
>
> Reported-by: syzbot+df038d463cca332e8414@...kaller.appspotmail.com
> Link: https://lore.kernel.org/all/0000000000005be0aa061846f8d6@google.com/
> Reported-by: syzbot+d7c7a495a5e466c031b6@...kaller.appspotmail.com
> Link: https://lore.kernel.org/all/000000000000b86c5e06130da9c6@google.com/
> Reported-by: syzbot+1527696d41a634cc1819@...kaller.appspotmail.com
> Link: https://lore.kernel.org/all/000000000000041f960618206d7e@google.com/
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Eric Van Hensbergen <ericvh@...nel.org>
> cc: Latchesar Ionkov <lucho@...kov.net>
> cc: Dominique Martinet <asmadeus@...ewreck.org>
With these two nitpicks in commit message addressed, looks good to me,
thanks!
Reviewed-by: Dominique Martinet <asmadeus@...ewreck.org>
> cc: Christian Schoenebeck <linux_oss@...debyte.com>
> cc: Jeff Layton <jlayton@...nel.org>
> cc: Steve French <sfrench@...ba.org>
> cc: Hillf Danton <hdanton@...a.com>
> cc: v9fs@...ts.linux.dev
> cc: linux-afs@...ts.infradead.org
> cc: linux-cifs@...r.kernel.org
> cc: netfs@...ts.linux.dev
> cc: linux-fsdevel@...r.kernel.org
>
> Notes:
> Changes
> =======
> ver #2)
> - Wait for outstanding I/O before clobbering the pagecache.
>
> ---
> fs/9p/vfs_inode.c | 1 +
> fs/afs/inode.c | 1 +
> fs/netfs/objects.c | 5 +++++
> fs/smb/client/cifsfs.c | 1 +
> include/linux/netfs.h | 18 ++++++++++++++++++
> 5 files changed, 26 insertions(+)
>
> diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
> index 8c9a896d691e..effb3aa1f3ed 100644
> --- a/fs/9p/vfs_inode.c
> +++ b/fs/9p/vfs_inode.c
> @@ -349,6 +349,7 @@ void v9fs_evict_inode(struct inode *inode)
> __le32 __maybe_unused version;
>
> if (!is_bad_inode(inode)) {
> + netfs_wait_for_outstanding_io(inode);
> truncate_inode_pages_final(&inode->i_data);
>
> version = cpu_to_le32(v9inode->qid.version);
> diff --git a/fs/afs/inode.c b/fs/afs/inode.c
> index 94fc049aff58..15bb7989c387 100644
> --- a/fs/afs/inode.c
> +++ b/fs/afs/inode.c
> @@ -648,6 +648,7 @@ void afs_evict_inode(struct inode *inode)
>
> ASSERTCMP(inode->i_ino, ==, vnode->fid.vnode);
>
> + netfs_wait_for_outstanding_io(inode);
> truncate_inode_pages_final(&inode->i_data);
>
> afs_set_cache_aux(vnode, &aux);
> diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
> index c90d482b1650..f4a642727479 100644
> --- a/fs/netfs/objects.c
> +++ b/fs/netfs/objects.c
> @@ -72,6 +72,7 @@ struct netfs_io_request *netfs_alloc_request(struct address_space *mapping,
> }
> }
>
> + atomic_inc(&ctx->io_count);
> trace_netfs_rreq_ref(rreq->debug_id, 1, netfs_rreq_trace_new);
> netfs_proc_add_rreq(rreq);
> netfs_stat(&netfs_n_rh_rreq);
> @@ -124,6 +125,7 @@ static void netfs_free_request(struct work_struct *work)
> {
> struct netfs_io_request *rreq =
> container_of(work, struct netfs_io_request, work);
> + struct netfs_inode *ictx = netfs_inode(rreq->inode);
> unsigned int i;
>
> trace_netfs_rreq(rreq, netfs_rreq_trace_free);
> @@ -142,6 +144,9 @@ static void netfs_free_request(struct work_struct *work)
> }
> kvfree(rreq->direct_bv);
> }
> +
> + if (atomic_dec_and_test(&ictx->io_count))
> + wake_up_var(&ictx->io_count);
> call_rcu(&rreq->rcu, netfs_free_request_rcu);
> }
>
> diff --git a/fs/smb/client/cifsfs.c b/fs/smb/client/cifsfs.c
> index ec5b639f421a..14810ffd15c8 100644
> --- a/fs/smb/client/cifsfs.c
> +++ b/fs/smb/client/cifsfs.c
> @@ -431,6 +431,7 @@ cifs_free_inode(struct inode *inode)
> static void
> cifs_evict_inode(struct inode *inode)
> {
> + netfs_wait_for_outstanding_io(inode);
> truncate_inode_pages_final(&inode->i_data);
> if (inode->i_state & I_PINNING_NETFS_WB)
> cifs_fscache_unuse_inode_cookie(inode, true);
> diff --git a/include/linux/netfs.h b/include/linux/netfs.h
> index d2d291a9cdad..3ca3906bb8da 100644
> --- a/include/linux/netfs.h
> +++ b/include/linux/netfs.h
> @@ -68,6 +68,7 @@ struct netfs_inode {
> loff_t remote_i_size; /* Size of the remote file */
> loff_t zero_point; /* Size after which we assume there's no data
> * on the server */
> + atomic_t io_count; /* Number of outstanding reqs */
> unsigned long flags;
> #define NETFS_ICTX_ODIRECT 0 /* The file has DIO in progress */
> #define NETFS_ICTX_UNBUFFERED 1 /* I/O should not use the pagecache */
> @@ -474,6 +475,7 @@ static inline void netfs_inode_init(struct netfs_inode *ctx,
> ctx->remote_i_size = i_size_read(&ctx->inode);
> ctx->zero_point = LLONG_MAX;
> ctx->flags = 0;
> + atomic_set(&ctx->io_count, 0);
> #if IS_ENABLED(CONFIG_FSCACHE)
> ctx->cache = NULL;
> #endif
> @@ -517,4 +519,20 @@ static inline struct fscache_cookie *netfs_i_cookie(struct netfs_inode *ctx)
> #endif
> }
>
> +/**
> + * netfs_wait_for_outstanding_io - Wait for outstanding I/O to complete
> + * @ctx: The netfs inode to wait on
> + *
> + * Wait for outstanding I/O requests of any type to complete. This is intended
> + * to be called from inode eviction routines. This makes sure that any
> + * resources held by those requests are cleaned up before we let the inode get
> + * cleaned up.
> + */
> +static inline void netfs_wait_for_outstanding_io(struct inode *inode)
> +{
> + struct netfs_inode *ictx = netfs_inode(inode);
> +
> + wait_var_event(&ictx->io_count, atomic_read(&ictx->io_count) == 0);
> +}
> +
> #endif /* _LINUX_NETFS_H */
>
--
Dominique Martinet | Asmadeus
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