smb: Fix regression in writes when non-standard maximum write size negotiated

The conversion to netfs in the 6.3 kernel caused a regression when
maximum write size is set by the server to an unexpected value which is
not a multiple of 4096 (similarly if the user overrides the maximum
write size by setting mount parm "wsize", but sets it to a value that
is not a multiple of 4096).  When negotiated write size is not a
multiple of 4096 the netfs code can skip the end of the final
page when doing large sequential writes, causing data corruption.

This section of code is being rewritten/removed due to a large
netfs change, but until that point (ie for the 6.3 kernel until now)
we can not support non-standard maximum write sizes.

Add a warning if a user specifies a wsize on mount that is not
a multiple of 4096 (and round down), also add a change where we
round down the maximum write size if the server negotiates a value
that is not a multiple of 4096 (we also have to check to make sure that
we do not round it down to zero).

Reported-by: R. Diez" <rdiez-2006@rd10.de>
Fixes: d08089f649a0 ("cifs: Change the I/O paths to use an iterator rather than a page list")
Suggested-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Acked-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Tested-by: Matthew Ruffell <matthew.ruffell@canonical.com>
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Cc: stable@vger.kernel.org # v6.3+
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c
index d03253f8f14552074dc79726a8d6521412eba6c4..ac9595504f4b11fa066a6516f034bff8bc09d56b 100644 (file)
--- a/fs/smb/client/connect.c
+++ b/fs/smb/client/connect.c
@@ -3444,8 +3444,18 @@ int cifs_mount_get_tcon(struct cifs_mount_ctx *mnt_ctx)
         * the user on mount
         */
        if ((cifs_sb->ctx->wsize == 0) ||
-           (cifs_sb->ctx->wsize > server->ops->negotiate_wsize(tcon, ctx)))
-               cifs_sb->ctx->wsize = server->ops->negotiate_wsize(tcon, ctx);
+           (cifs_sb->ctx->wsize > server->ops->negotiate_wsize(tcon, ctx))) {
+               cifs_sb->ctx->wsize =
+                       round_down(server->ops->negotiate_wsize(tcon, ctx), PAGE_SIZE);
+               /*
+                * in the very unlikely event that the server sent a max write size under PAGE_SIZE,
+                * (which would get rounded down to 0) then reset wsize to absolute minimum eg 4096
+                */
+               if (cifs_sb->ctx->wsize == 0) {
+                       cifs_sb->ctx->wsize = PAGE_SIZE;
+                       cifs_dbg(VFS, "wsize too small, reset to minimum ie PAGE_SIZE, usually 4096\n");
+               }
+       }
        if ((cifs_sb->ctx->rsize == 0) ||
            (cifs_sb->ctx->rsize > server->ops->negotiate_rsize(tcon, ctx)))
                cifs_sb->ctx->rsize = server->ops->negotiate_rsize(tcon, ctx);

diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
index aec8dbd1f9dbd2b685219850c65b0695ba657aba..4b2f5aa2ea0e1de026302b9e543e2e13429107f9 100644 (file)
--- a/fs/smb/client/fs_context.c
+++ b/fs/smb/client/fs_context.c
@@ -1111,6 +1111,17 @@ static int smb3_fs_context_parse_param(struct fs_context *fc,
        case Opt_wsize:
                ctx->wsize = result.uint_32;
                ctx->got_wsize = true;
+               if (ctx->wsize % PAGE_SIZE != 0) {
+                       ctx->wsize = round_down(ctx->wsize, PAGE_SIZE);
+                       if (ctx->wsize == 0) {
+                               ctx->wsize = PAGE_SIZE;
+                               cifs_dbg(VFS, "wsize too small, reset to minimum %ld\n", PAGE_SIZE);
+                       } else {
+                               cifs_dbg(VFS,
+                                        "wsize rounded down to %d to multiple of PAGE_SIZE %ld\n",
+                                        ctx->wsize, PAGE_SIZE);
+                       }
+               }
                break;
        case Opt_acregmax:
                ctx->acregmax = HZ * result.uint_32;