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>

1 files changed, 11 insertions, 0 deletions

diff --git a/fs/smb/client/fs_context.c b/fs/smb/client/fs_context.c
index aec8dbd1f9db..4b2f5aa2ea0e 100644
--- 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;