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file: In f_dupfd read RLIMIT_NOFILE once. 

Simplify the code, and remove the chance of races by reading
RLIMIT_NOFILE only once in f_dupfd.

Pass the read value of RLIMIT_NOFILE into alloc_fd which is the other
location the rlimit was read in f_dupfd.  As f_dupfd is the only
caller of alloc_fd this changing alloc_fd is trivially safe.

Further this causes alloc_fd to take all of the same arguments as
__alloc_fd except for the files_struct argument.

Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
v1: https://lkml.kernel.org/r/20200817220425.9389-15-ebiederm@xmission.com
Link: https://lkml.kernel.org/r/20201120231441.29911-19-ebiederm@xmission.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2020-11-20 17:14:36 -06:00
parent d74ba04d91
commit e06b53c22f
1 changed files with 5 additions and 4 deletions
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9
fs/file.c
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@ -538,9 +538,9 @@ int __alloc_fd(struct files_struct *files,
return error;
}
static int alloc_fd(unsigned start, unsigned flags)
static int alloc_fd(unsigned start, unsigned end, unsigned flags)
{
return __alloc_fd(current->files, start, rlimit(RLIMIT_NOFILE), flags);
return __alloc_fd(current->files, start, end, flags);
}
int __get_unused_fd_flags(unsigned flags, unsigned long nofile)
@ -1175,10 +1175,11 @@ SYSCALL_DEFINE1(dup, unsigned int, fildes)
int f_dupfd(unsigned int from, struct file *file, unsigned flags)
{
unsigned long nofile = rlimit(RLIMIT_NOFILE);
int err;
if (from >= rlimit(RLIMIT_NOFILE))
if (from >= nofile)
return -EINVAL;
err = alloc_fd(from, flags);
err = alloc_fd(from, nofile, flags);
if (err >= 0) {
get_file(file);
fd_install(err, file);