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fs: use do_splice_direct() for nfsd/ksmbd server-side-copy

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nfsd/ksmbd call vfs_copy_file_range() with flag COPY_FILE_SPLICE to
perform kernel copy between two files on any two filesystems.

Splicing input file, while holding file_start_write() on the output file
which is on a different sb, posses a risk for fanotify related deadlocks.

We only need to call splice_file_range() from within the context of
->copy_file_range() filesystem methods with file_start_write() held.

To avoid the possible deadlocks, always use do_splice_direct() instead of
splice_file_range() for the kernel copy fallback in vfs_copy_file_range()
without holding file_start_write().

Reported-and-tested-by: Bert Karwatzki <spasswolf@web.de>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20231130141624.3338942-4-amir73il@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Amir Goldstein 2023-11-30 16:16:24 +02:00 committed by Christian Brauner
parent da40448ce4
commit 7306512686
1 changed files with 26 additions and 13 deletions
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39
fs/read_write.c
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@ -1421,6 +1421,10 @@ ssize_t generic_copy_file_range(struct file *file_in, loff_t pos_in,
struct file *file_out, loff_t pos_out,
size_t len, unsigned int flags)
{
/* May only be called from within ->copy_file_range() methods */
if (WARN_ON_ONCE(flags))
return -EINVAL;
return splice_file_range(file_in, &pos_in, file_out, &pos_out,
min_t(size_t, len, MAX_RW_COUNT));
}
@ -1510,6 +1514,7 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
{
ssize_t ret;
bool splice = flags & COPY_FILE_SPLICE;
bool samesb = file_inode(file_in)->i_sb == file_inode(file_out)->i_sb;
if (flags & ~COPY_FILE_SPLICE)
return -EINVAL;
@ -1541,19 +1546,24 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
ret = file_out->f_op->copy_file_range(file_in, pos_in,
file_out, pos_out,
len, flags);
goto done;
}
if (!splice && file_in->f_op->remap_file_range &&
file_inode(file_in)->i_sb == file_inode(file_out)->i_sb) {
} else if (!splice && file_in->f_op->remap_file_range && samesb) {
ret = file_in->f_op->remap_file_range(file_in, pos_in,
file_out, pos_out,
min_t(loff_t, MAX_RW_COUNT, len),
REMAP_FILE_CAN_SHORTEN);
if (ret > 0)
goto done;
/* fallback to splice */
if (ret <= 0)
splice = true;
} else if (samesb) {
/* Fallback to splice for same sb copy for backward compat */
splice = true;
}
file_end_write(file_out);
if (!splice)
goto done;
/*
* We can get here for same sb copy of filesystems that do not implement
* ->copy_file_range() in case filesystem does not support clone or in
@ -1565,11 +1575,16 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
* and which filesystems do not, that will allow userspace tools to
* make consistent desicions w.r.t using copy_file_range().
*
* We also get here if caller (e.g. nfsd) requested COPY_FILE_SPLICE.
* We also get here if caller (e.g. nfsd) requested COPY_FILE_SPLICE
* for server-side-copy between any two sb.
*
* In any case, we call do_splice_direct() and not splice_file_range(),
* without file_start_write() held, to avoid possible deadlocks related
* to splicing from input file, while file_start_write() is held on
* the output file on a different sb.
*/
ret = generic_copy_file_range(file_in, pos_in, file_out, pos_out, len,
flags);
ret = do_splice_direct(file_in, &pos_in, file_out, &pos_out,
min_t(size_t, len, MAX_RW_COUNT), 0);
done:
if (ret > 0) {
fsnotify_access(file_in);
@ -1581,8 +1596,6 @@ done:
inc_syscr(current);
inc_syscw(current);
file_end_write(file_out);
return ret;
}
EXPORT_SYMBOL(vfs_copy_file_range);