From: Udipto Goswami quic_ugoswami@quicinc.com
[ Upstream commit ebe2b1add1055b903e2acd86b290a85297edc0b3 ]
Consider a case where ffs_func_eps_disable is called from ffs_func_disable as part of composition switch and at the same time ffs_epfile_release get called from userspace. ffs_epfile_release will free up the read buffer and call ffs_data_closed which in turn destroys ffs->epfiles and mark it as NULL. While this was happening the driver has already initialized the local epfile in ffs_func_eps_disable which is now freed and waiting to acquire the spinlock. Once spinlock is acquired the driver proceeds with the stale value of epfile and tries to free the already freed read buffer causing use-after-free.
Following is the illustration of the race:
CPU1 CPU2
ffs_func_eps_disable epfiles (local copy) ffs_epfile_release ffs_data_closed if (last file closed) ffs_data_reset ffs_data_clear ffs_epfiles_destroy spin_lock dereference epfiles
Fix this races by taking epfiles local copy & assigning it under spinlock and if epfiles(local) is null then update it in ffs->epfiles then finally destroy it. Extending the scope further from the race, protecting the ep related structures, and concurrent accesses.
Fixes: a9e6f83c2df1 ("usb: gadget: f_fs: stop sleeping in ffs_func_eps_disable") Co-developed-by: Udipto Goswami quic_ugoswami@quicinc.com Reviewed-by: John Keeping john@metanate.com Signed-off-by: Pratham Pratap quic_ppratap@quicinc.com Signed-off-by: Udipto Goswami quic_ugoswami@quicinc.com Link: https://lore.kernel.org/r/1643256595-10797-1-git-send-email-quic_ugoswami@qu... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/usb/gadget/function/f_fs.c | 56 ++++++++++++++++++++++-------- 1 file changed, 42 insertions(+), 14 deletions(-)
diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c index 25ad1e97a4585..1922fd02043c5 100644 --- a/drivers/usb/gadget/function/f_fs.c +++ b/drivers/usb/gadget/function/f_fs.c @@ -1711,16 +1711,24 @@ static void ffs_data_put(struct ffs_data *ffs)
static void ffs_data_closed(struct ffs_data *ffs) { + struct ffs_epfile *epfiles; + unsigned long flags; + ENTER();
if (atomic_dec_and_test(&ffs->opened)) { if (ffs->no_disconnect) { ffs->state = FFS_DEACTIVATED; - if (ffs->epfiles) { - ffs_epfiles_destroy(ffs->epfiles, - ffs->eps_count); - ffs->epfiles = NULL; - } + spin_lock_irqsave(&ffs->eps_lock, flags); + epfiles = ffs->epfiles; + ffs->epfiles = NULL; + spin_unlock_irqrestore(&ffs->eps_lock, + flags); + + if (epfiles) + ffs_epfiles_destroy(epfiles, + ffs->eps_count); + if (ffs->setup_state == FFS_SETUP_PENDING) __ffs_ep0_stall(ffs); } else { @@ -1767,14 +1775,27 @@ static struct ffs_data *ffs_data_new(const char *dev_name)
static void ffs_data_clear(struct ffs_data *ffs) { + struct ffs_epfile *epfiles; + unsigned long flags; + ENTER();
ffs_closed(ffs);
BUG_ON(ffs->gadget);
- if (ffs->epfiles) { - ffs_epfiles_destroy(ffs->epfiles, ffs->eps_count); + spin_lock_irqsave(&ffs->eps_lock, flags); + epfiles = ffs->epfiles; + ffs->epfiles = NULL; + spin_unlock_irqrestore(&ffs->eps_lock, flags); + + /* + * potential race possible between ffs_func_eps_disable + * & ffs_epfile_release therefore maintaining a local + * copy of epfile will save us from use-after-free. + */ + if (epfiles) { + ffs_epfiles_destroy(epfiles, ffs->eps_count); ffs->epfiles = NULL; }
@@ -1922,12 +1943,15 @@ static void ffs_epfiles_destroy(struct ffs_epfile *epfiles, unsigned count)
static void ffs_func_eps_disable(struct ffs_function *func) { - struct ffs_ep *ep = func->eps; - struct ffs_epfile *epfile = func->ffs->epfiles; - unsigned count = func->ffs->eps_count; + struct ffs_ep *ep; + struct ffs_epfile *epfile; + unsigned short count; unsigned long flags;
spin_lock_irqsave(&func->ffs->eps_lock, flags); + count = func->ffs->eps_count; + epfile = func->ffs->epfiles; + ep = func->eps; while (count--) { /* pending requests get nuked */ if (ep->ep) @@ -1945,14 +1969,18 @@ static void ffs_func_eps_disable(struct ffs_function *func)
static int ffs_func_eps_enable(struct ffs_function *func) { - struct ffs_data *ffs = func->ffs; - struct ffs_ep *ep = func->eps; - struct ffs_epfile *epfile = ffs->epfiles; - unsigned count = ffs->eps_count; + struct ffs_data *ffs; + struct ffs_ep *ep; + struct ffs_epfile *epfile; + unsigned short count; unsigned long flags; int ret = 0;
spin_lock_irqsave(&func->ffs->eps_lock, flags); + ffs = func->ffs; + ep = func->eps; + epfile = ffs->epfiles; + count = ffs->eps_count; while(count--) { ep->ep->driver_data = ep;