afs: Fix StoreData op marshalling

dhowells · torvalds · commit 8c7ae38d1ce1 · 2019-03-28T08:54:20.000-07:00
The marshalling of AFS.StoreData, AFS.StoreData64 and YFS.StoreData64 calls generated by ->setattr() ops for the purpose of expanding a file is incorrect due to older documentation incorrectly describing the way the RPC 'FileLength' parameter is meant to work. The older documentation says that this is the length the file is meant to end up at the end of the operation; however, it was never implemented this way in any of the servers, but rather the file is truncated down to this before the write operation is effected, and never expanded to it (and, indeed, it was renamed to 'TruncPos' in 2014). Fix this by setting the position parameter to the new file length and doing a zero-lengh write there. The bug causes Xwayland to SIGBUS due to unexpected non-expansion of a file it then mmaps. This can be tested by giving the following test program a filename in an AFS directory: #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h> #include <sys/mman.h> int main(int argc, char *argv[]) { char *p; int fd; if (argc != 2) { fprintf(stderr, "Format: test-trunc-mmap <file>\n"); exit(2); } fd = open(argv[1], O_RDWR | O_CREAT | O_TRUNC); if (fd < 0) { perror(argv[1]); exit(1); } if (ftruncate(fd, 0x140008) == -1) { perror("ftruncate"); exit(1); } p = mmap(NULL, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); if (p == MAP_FAILED) { perror("mmap"); exit(1); } p[0] = 'a'; if (munmap(p, 4096) < 0) { perror("munmap"); exit(1); } if (close(fd) < 0) { perror("close"); exit(1); } exit(0); } Fixes: 31143d5 ("AFS: implement basic file write support") Reported-by: Jonathan Billings <jsbillin@umich.edu> Tested-by: Jonathan Billings <jsbillin@umich.edu> Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/afs/fsclient.c b/fs/afs/fsclient.c
@@ -1515,8 +1515,8 @@ static int afs_fs_setattr_size64(struct afs_fs_cursor *fc, struct iattr *attr)
 
 	xdr_encode_AFS_StoreStatus(&bp, attr);
 
-	*bp++ = 0;				/* position of start of write */
-	*bp++ = 0;
+	*bp++ = htonl(attr->ia_size >> 32);	/* position of start of write */
+	*bp++ = htonl((u32) attr->ia_size);
 	*bp++ = 0;				/* size of write */
 	*bp++ = 0;
 	*bp++ = htonl(attr->ia_size >> 32);	/* new file length */
@@ -1564,7 +1564,7 @@ static int afs_fs_setattr_size(struct afs_fs_cursor *fc, struct iattr *attr)
 
 	xdr_encode_AFS_StoreStatus(&bp, attr);
 
-	*bp++ = 0;				/* position of start of write */
+	*bp++ = htonl(attr->ia_size);		/* position of start of write */
 	*bp++ = 0;				/* size of write */
 	*bp++ = htonl(attr->ia_size);		/* new file length */
 
diff --git a/fs/afs/yfsclient.c b/fs/afs/yfsclient.c
@@ -1514,7 +1514,7 @@ static int yfs_fs_setattr_size(struct afs_fs_cursor *fc, struct iattr *attr)
 	bp = xdr_encode_u32(bp, 0); /* RPC flags */
 	bp = xdr_encode_YFSFid(bp, &vnode->fid);
 	bp = xdr_encode_YFS_StoreStatus(bp, attr);
-	bp = xdr_encode_u64(bp, 0);		/* position of start of write */
+	bp = xdr_encode_u64(bp, attr->ia_size);	/* position of start of write */
 	bp = xdr_encode_u64(bp, 0);		/* size of write */
 	bp = xdr_encode_u64(bp, attr->ia_size);	/* new file length */
 	yfs_check_req(call, bp);
