cifs: fix oops during encryption

When running xfstests against Azure the following oops occurred on an
arm64 system

  Unable to handle kernel write to read-only memory at virtual address
  ffff0001221cf000
  Mem abort info:
    ESR = 0x9600004f
    EC = 0x25: DABT (current EL), IL = 32 bits
    SET = 0, FnV = 0
    EA = 0, S1PTW = 0
    FSC = 0x0f: level 3 permission fault
  Data abort info:
    ISV = 0, ISS = 0x0000004f
    CM = 0, WnR = 1
  swapper pgtable: 4k pages, 48-bit VAs, pgdp=00000000294f3000
  [ffff0001221cf000] pgd=18000001ffff8003, p4d=18000001ffff8003,
  pud=18000001ff82e003, pmd=18000001ff71d003, pte=00600001221cf787
  Internal error: Oops: 9600004f [#1] PREEMPT SMP
  ...
  pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--)
  pc : __memcpy+0x40/0x230
  lr : scatterwalk_copychunks+0xe0/0x200
  sp : ffff800014e92de0
  x29: ffff800014e92de0 x28: ffff000114f9de80 x27: 0000000000000008
  x26: 0000000000000008 x25: ffff800014e92e78 x24: 0000000000000008
  x23: 0000000000000001 x22: 0000040000000000 x21: ffff000000000000
  x20: 0000000000000001 x19: ffff0001037c4488 x18: 0000000000000014
  x17: 235e1c0d6efa9661 x16: a435f9576b6edd6c x15: 0000000000000058
  x14: 0000000000000001 x13: 0000000000000008 x12: ffff000114f2e590
  x11: ffffffffffffffff x10: 0000040000000000 x9 : ffff8000105c3580
  x8 : 2e9413b10000001a x7 : 534b4410fb86b005 x6 : 534b4410fb86b005
  x5 : ffff0001221cf008 x4 : ffff0001037c4490 x3 : 0000000000000001
  x2 : 0000000000000008 x1 : ffff0001037c4488 x0 : ffff0001221cf000
  Call trace:
   __memcpy+0x40/0x230
   scatterwalk_map_and_copy+0x98/0x100
   crypto_ccm_encrypt+0x150/0x180
   crypto_aead_encrypt+0x2c/0x40
   crypt_message+0x750/0x880
   smb3_init_transform_rq+0x298/0x340
   smb_send_rqst.part.11+0xd8/0x180
   smb_send_rqst+0x3c/0x100
   compound_send_recv+0x534/0xbc0
   smb2_query_info_compound+0x32c/0x440
   smb2_set_ea+0x438/0x4c0
   cifs_xattr_set+0x5d4/0x7c0

This is because in scatterwalk_copychunks(), we attempted to write to
a buffer (@sign) that was allocated in the stack (vmalloc area) by
crypt_message() and thus accessing its remaining 8 (x2) bytes ended up
crossing a page boundary.

To simply fix it, we could just pass @sign kmalloc'd from
crypt_message() and then we're done.  Luckily, we don't seem to pass
any other vmalloc'd buffers in smb_rqst::rq_iov...

Instead, let's map the correct pages and offsets from vmalloc buffers
as well in cifs_sg_set_buf() and then avoiding such oopses.

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 68 insertions, 0 deletions

diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index cd3a173e65b1..703685e2db5e 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -13,6 +13,8 @@
 #include <linux/in6.h>
 #include <linux/inet.h>
 #include <linux/slab.h>
+#include <linux/scatterlist.h>
+#include <linux/mm.h>
 #include <linux/mempool.h>
 #include <linux/workqueue.h>
 #include <linux/utsname.h>
@@ -2140,4 +2142,70 @@ static inline void move_cifs_info_to_smb2(struct smb2_file_all_info *dst, const
 	dst->FileNameLength = src->FileNameLength;
 }
 
+static inline unsigned int cifs_get_num_sgs(const struct smb_rqst *rqst,
+					    int num_rqst,
+					    const u8 *sig)
+{
+	unsigned int len, skip;
+	unsigned int nents = 0;
+	unsigned long addr;
+	int i, j;
+
+	/* Assumes the first rqst has a transform header as the first iov.
+	 * I.e.
+	 * rqst[0].rq_iov[0]  is transform header
+	 * rqst[0].rq_iov[1+] data to be encrypted/decrypted
+	 * rqst[1+].rq_iov[0+] data to be encrypted/decrypted
+	 */
+	for (i = 0; i < num_rqst; i++) {
+		/*
+		 * The first rqst has a transform header where the
+		 * first 20 bytes are not part of the encrypted blob.
+		 */
+		for (j = 0; j < rqst[i].rq_nvec; j++) {
+			struct kvec *iov = &rqst[i].rq_iov[j];
+
+			skip = (i == 0) && (j == 0) ? 20 : 0;
+			addr = (unsigned long)iov->iov_base + skip;
+			if (unlikely(is_vmalloc_addr((void *)addr))) {
+				len = iov->iov_len - skip;
+				nents += DIV_ROUND_UP(offset_in_page(addr) + len,
+						      PAGE_SIZE);
+			} else {
+				nents++;
+			}
+		}
+		nents += rqst[i].rq_npages;
+	}
+	nents += DIV_ROUND_UP(offset_in_page(sig) + SMB2_SIGNATURE_SIZE, PAGE_SIZE);
+	return nents;
+}
+
+/* We can not use the normal sg_set_buf() as we will sometimes pass a
+ * stack object as buf.
+ */
+static inline struct scatterlist *cifs_sg_set_buf(struct scatterlist *sg,
+						  const void *buf,
+						  unsigned int buflen)
+{
+	unsigned long addr = (unsigned long)buf;
+	unsigned int off = offset_in_page(addr);
+
+	addr &= PAGE_MASK;
+	if (unlikely(is_vmalloc_addr((void *)addr))) {
+		do {
+			unsigned int len = min_t(unsigned int, buflen, PAGE_SIZE - off);
+
+			sg_set_page(sg++, vmalloc_to_page((void *)addr), len, off);
+
+			off = 0;
+			addr += PAGE_SIZE;
+			buflen -= len;
+		} while (buflen);
+	} else {
+		sg_set_page(sg++, virt_to_page(addr), buflen, off);
+	}
+	return sg;
+}
+
 #endif	/* _CIFS_GLOB_H */