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fuse: fix fuse_send_readpages() in the syncronous read case 

commit 7df1e988c7 upstream.

Buffered read in fuse normally goes via:

 -> generic_file_buffered_read()
   -> fuse_readpages()
     -> fuse_send_readpages()
       ->fuse_simple_request() [called since v5.4]

In the case of a read request, fuse_simple_request() will return a
non-negative bytecount on success or a negative error value.  A positive
bytecount was taken to be an error and the PG_error flag set on the page.
This resulted in generic_file_buffered_read() falling back to ->readpage(),
which would repeat the read request and succeed.  Because of the repeated
read succeeding the bug was not detected with regression tests or other use
cases.

The FTP module in GVFS however fails the second read due to the
non-seekable nature of FTP downloads.

Fix by checking and ignoring positive return value from
fuse_simple_request().

Reported-by: Ondrej Holy <oholy@redhat.com>
Link: https://gitlab.gnome.org/GNOME/gvfs/issues/441
Fixes: 134831e36b ("fuse: convert readpages to simple api")
Cc: <stable@vger.kernel.org> # v5.4
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Miklos Szeredi 2020-01-16 11:09:36 +01:00 committed by Greg Kroah-Hartman
parent 6eed26e35c
commit 7e7f29200f
1 changed files with 3 additions and 1 deletions
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4
fs/fuse/file.c
View File

@ -882,6 +882,7 @@ static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file)
struct fuse_args_pages *ap = &ia->ap;
loff_t pos = page_offset(ap->pages[0]);
size_t count = ap->num_pages << PAGE_SHIFT;
ssize_t res;
int err;
ap->args.out_pages = true;
@ -896,7 +897,8 @@ static void fuse_send_readpages(struct fuse_io_args *ia, struct file *file)
if (!err)
return;
} else {
err = fuse_simple_request(fc, &ap->args);
res = fuse_simple_request(fc, &ap->args);
err = res < 0 ? res : 0;
}
fuse_readpages_end(fc, &ap->args, err);
}