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authorAl Viro <viro@zeniv.linux.org.uk>2008-04-27 20:04:15 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2008-05-01 13:08:57 -0400
commit5c598b3428c372a1209597cee99a70da20625876 (patch)
tree2ab9df5d60471e28074e97dca3c97b8c37d626b3 /fs/file.c
parent2030a42cecd4dd1985a2ab03e25f3cd6106a5ca8 (diff)
downloadlwn-5c598b3428c372a1209597cee99a70da20625876.tar.gz
lwn-5c598b3428c372a1209597cee99a70da20625876.zip
[PATCH] fix sysctl_nr_open bugs
* if luser with root sets it to something that is not a multiple of BITS_PER_LONG, the system is screwed. * if it gets decreased at the wrong time, we can get expand_files() returning success and _not_ increasing the size of table as asked. Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/file.c')
-rw-r--r--fs/file.c22
1 files changed, 20 insertions, 2 deletions
diff --git a/fs/file.c b/fs/file.c
index f6fbcb49faf7..4c6f0ea12c41 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -150,8 +150,16 @@ static struct fdtable * alloc_fdtable(unsigned int nr)
nr /= (1024 / sizeof(struct file *));
nr = roundup_pow_of_two(nr + 1);
nr *= (1024 / sizeof(struct file *));
- if (nr > sysctl_nr_open)
- nr = sysctl_nr_open;
+ /*
+ * Note that this can drive nr *below* what we had passed if sysctl_nr_open
+ * had been set lower between the check in expand_files() and here. Deal
+ * with that in caller, it's cheaper that way.
+ *
+ * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
+ * bitmaps handling below becomes unpleasant, to put it mildly...
+ */
+ if (unlikely(nr > sysctl_nr_open))
+ nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;
fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
if (!fdt)
@@ -200,6 +208,16 @@ static int expand_fdtable(struct files_struct *files, int nr)
if (!new_fdt)
return -ENOMEM;
/*
+ * extremely unlikely race - sysctl_nr_open decreased between the check in
+ * caller and alloc_fdtable(). Cheaper to catch it here...
+ */
+ if (unlikely(new_fdt->max_fds <= nr)) {
+ free_fdarr(new_fdt);
+ free_fdset(new_fdt);
+ kfree(new_fdt);
+ return -EMFILE;
+ }
+ /*
* Check again since another task may have expanded the fd table while
* we dropped the lock
*/