@@ -1517,6 +1517,17 @@ CIFSSMBWrite(const int xid, struct cifsTconInfo *tcon,
*nbytes = le16_to_cpu(pSMBr->CountHigh);
*nbytes = (*nbytes) << 16;
*nbytes += le16_to_cpu(pSMBr->Count);
+
+ /*
+ * Workaround: Some legacy servers (read OS/2) might incorrectly
+ * set CountHigh for normal writes resulting in wrong 'nbytes'
+ * value. So when the write returns successfully and the bytes
+ * written as returned by the server is greater than bytes
+ * requested, reset it to original bytes requested.
+ */
+
+ if (*nbytes > count)
+ *nbytes = count;
}
cifs_buf_release(pSMB);
@@ -1605,6 +1616,17 @@ CIFSSMBWrite2(const int xid, struct cifsTconInfo *tcon,
*nbytes = le16_to_cpu(pSMBr->CountHigh);
*nbytes = (*nbytes) << 16;
*nbytes += le16_to_cpu(pSMBr->Count);
+
+ /*
+ * Workaround: Some legacy servers (read OS/2) might incorrectly
+ * set CountHigh for normal writes resulting in wrong 'nbytes'
+ * value. So when the write returns successfully and the bytes
+ * written as returned by the server is greater than bytes
+ * requested, reset it to original bytes requested.
+ */
+
+ if (*nbytes > count)
+ *nbytes = count;
}
/* cifs_small_buf_release(pSMB); */ /* Freed earlier now in SendReceive2 */
While chasing a bug report involving a OS/2 server, I noticed the server sets pSMBr->CountHigh to a incorrect value even in case of normal writes. This leads to 'nbytes' being computed wrongly and triggers a kernel BUG at mm/filemap.c. void iov_iter_advance(struct iov_iter *i, size_t bytes) { BUG_ON(i->count < bytes); <--- BUG here Why the server is setting 'CountHigh' is not clear but only does so after writing 64k bytes. Though this looks like the server bug, the client side crash may not be acceptable. When the write returns successfully and the bytes written as returned by the server is greater than bytes requested by the client, reset it to original bytes requested. Cc: Jeff Layton <jlayton@samba.org> Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de> --- fs/cifs/cifssmb.c | 22 ++++++++++++++++++++++ 1 files changed, 22 insertions(+), 0 deletions(-)