5.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
commit 9a2fa1472083580b6c66bdaf291f591e1170123a upstream.
copy_fd_bitmaps(new, old, count) is expected to copy the first
count/BITS_PER_LONG bits from old->full_fds_bits[] and fill
the rest with zeroes. What it does is copying enough words
(BITS_TO_LONGS(count/BITS_PER_LONG)), then memsets the rest.
That works fine, *if* all bits past the cutoff point are
clear. Otherwise we are risking garbage from the last word
we'd copied.
For most of the callers that is true - expand_fdtable() has
count equal to old->max_fds, so there's no open descriptors
past count, let alone fully occupied words in ->open_fds[],
which is what bits in ->full_fds_bits[] correspond to.
The other caller (dup_fd()) passes sane_fdtable_size(old_fdt, max_fds),
which is the smallest multiple of BITS_PER_LONG that covers all
opened descriptors below max_fds. In the common case (copying on
fork()) max_fds is ~0U, so all opened descriptors will be below
it and we are fine, by the same reasons why the call in expand_fdtable()
is safe.
Unfortunately, there is a case where max_fds is less than that
and where we might, indeed, end up with junk in ->full_fds_bits[] -
close_range(from, to, CLOSE_RANGE_UNSHARE) with
* descriptor table being currently shared
* 'to' being above the current capacity of descriptor table
* 'from' being just under some chunk of opened descriptors.
In that case we end up with observably wrong behaviour - e.g. spawn
a child with CLONE_FILES, get all descriptors in range 0..127 open,
then close_range(64, ~0U, CLOSE_RANGE_UNSHARE) and watch dup(0) ending
up with descriptor #128, despite #64 being observably not open.
The minimally invasive fix would be to deal with that in dup_fd().
If this proves to add measurable overhead, we can go that way, but
let's try to fix copy_fd_bitmaps() first.
* new helper: bitmap_copy_and_expand(to, from, bits_to_copy, size).
* make copy_fd_bitmaps() take the bitmap size in words, rather than
bits; it's 'count' argument is always a multiple of BITS_PER_LONG,
so we are not losing any information, and that way we can use the
same helper for all three bitmaps - compiler will see that count
is a multiple of BITS_PER_LONG for the large ones, so it'll generate
plain memcpy()+memset().
Reproducer added to tools/testing/selftests/core/close_range_test.c
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/file.c | 28 ++++++++++++----------------
include/linux/bitmap.h | 12 ++++++++++++
2 files changed, 24 insertions(+), 16 deletions(-)
--- a/fs/file.c
+++ b/fs/file.c
@@ -41,27 +41,23 @@ static void free_fdtable_rcu(struct rcu_
#define BITBIT_NR(nr) BITS_TO_LONGS(BITS_TO_LONGS(nr))
#define BITBIT_SIZE(nr) (BITBIT_NR(nr) * sizeof(long))
+#define fdt_words(fdt) ((fdt)->max_fds / BITS_PER_LONG) // words in ->open_fds
/*
* Copy 'count' fd bits from the old table to the new table and clear the extra
* space if any. This does not copy the file pointers. Called with the files
* spinlock held for write.
*/
-static void copy_fd_bitmaps(struct fdtable *nfdt, struct fdtable *ofdt,
- unsigned int count)
+static inline void copy_fd_bitmaps(struct fdtable *nfdt, struct fdtable *ofdt,
+ unsigned int copy_words)
{
- unsigned int cpy, set;
+ unsigned int nwords = fdt_words(nfdt);
- cpy = count / BITS_PER_BYTE;
- set = (nfdt->max_fds - count) / BITS_PER_BYTE;
- memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
- memset((char *)nfdt->open_fds + cpy, 0, set);
- memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
- memset((char *)nfdt->close_on_exec + cpy, 0, set);
-
- cpy = BITBIT_SIZE(count);
- set = BITBIT_SIZE(nfdt->max_fds) - cpy;
- memcpy(nfdt->full_fds_bits, ofdt->full_fds_bits, cpy);
- memset((char *)nfdt->full_fds_bits + cpy, 0, set);
+ bitmap_copy_and_extend(nfdt->open_fds, ofdt->open_fds,
+ copy_words * BITS_PER_LONG, nwords * BITS_PER_LONG);
+ bitmap_copy_and_extend(nfdt->close_on_exec, ofdt->close_on_exec,
+ copy_words * BITS_PER_LONG, nwords * BITS_PER_LONG);
+ bitmap_copy_and_extend(nfdt->full_fds_bits, ofdt->full_fds_bits,
+ copy_words, nwords);
}
/*
@@ -79,7 +75,7 @@ static void copy_fdtable(struct fdtable
memcpy(nfdt->fd, ofdt->fd, cpy);
memset((char *)nfdt->fd + cpy, 0, set);
- copy_fd_bitmaps(nfdt, ofdt, ofdt->max_fds);
+ copy_fd_bitmaps(nfdt, ofdt, fdt_words(ofdt));
}
static struct fdtable * alloc_fdtable(unsigned int nr)
@@ -330,7 +326,7 @@ struct files_struct *dup_fd(struct files
open_files = count_open_files(old_fdt);
}
- copy_fd_bitmaps(new_fdt, old_fdt, open_files);
+ copy_fd_bitmaps(new_fdt, old_fdt, open_files / BITS_PER_LONG);
old_fds = old_fdt->fd;
new_fds = new_fdt->fd;
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -248,6 +248,18 @@ static inline void bitmap_copy_clear_tai
dst[nbits / BITS_PER_LONG] &= BITMAP_LAST_WORD_MASK(nbits);
}
+static inline void bitmap_copy_and_extend(unsigned long *to,
+ const unsigned long *from,
+ unsigned int count, unsigned int size)
+{
+ unsigned int copy = BITS_TO_LONGS(count);
+
+ memcpy(to, from, copy * sizeof(long));
+ if (count % BITS_PER_LONG)
+ to[copy - 1] &= BITMAP_LAST_WORD_MASK(count);
+ memset(to + copy, 0, bitmap_size(size) - copy * sizeof(long));
+}
+
/*
* On 32-bit systems bitmaps are represented as u32 arrays internally, and
* therefore conversion is not needed when copying data from/to arrays of u32.
