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authorAl Viro <viro@zeniv.linux.org.uk>2008-05-08 21:19:42 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2008-05-16 17:22:46 -0400
commitadbecb128cd2cc5d14b0ebef6d020ced0efd0ec6 (patch)
treeba0f7c202e364002eedc999526ac07262f21dae4
parentafbec7fff4928c273a1f1bb14dfdfdf62688a193 (diff)
[PATCH] dup_fd() part 4 - race fix
Parent _can_ be a clone task, contrary to the comment. Moreover, more files could be opened while we allocate a copy, in which case we end up copying only part into new descriptor table. Since what we get _is_ affected by all changes in the old range, we can get rather weird effects - e.g. dup2(0, 1024); close(0); in parallel with fork() resulting in child that sees the effect of close(), but not that of dup2() done just before that close(). What we need is to recalculate the open_count after having reacquired ->file_lock and if external fdtable we'd just allocated is too small for it, free the sucker and redo allocation. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r--fs/file.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/fs/file.c b/fs/file.c
index 689d2b6947e..0f705c7cfef 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -308,11 +308,16 @@ struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
/*
* Check whether we need to allocate a larger fd array and fd set.
- * Note: we're not a clone task, so the open count won't change.
*/
- if (open_files > new_fdt->max_fds) {
+ while (unlikely(open_files > new_fdt->max_fds)) {
spin_unlock(&oldf->file_lock);
+ if (new_fdt != &newf->fdtab) {
+ free_fdarr(new_fdt);
+ free_fdset(new_fdt);
+ kfree(new_fdt);
+ }
+
new_fdt = alloc_fdtable(open_files - 1);
if (!new_fdt) {
*errorp = -ENOMEM;
@@ -335,6 +340,7 @@ struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
*/
spin_lock(&oldf->file_lock);
old_fdt = files_fdtable(oldf);
+ open_files = count_open_files(old_fdt);
}
old_fds = old_fdt->fd;