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[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>
This commit is contained in:
Al Viro 2008-04-27 20:04:15 -04:00
parent 2030a42cec
commit 5c598b3428
1 changed files with 20 additions and 2 deletions
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22
fs/file.c
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@ -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)
@ -199,6 +207,16 @@ static int expand_fdtable(struct files_struct *files, int nr)
spin_lock(&files->file_lock);
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