On Fri, Jul 10, 2020 at 12:39:48AM +0200, Jann Horn wrote: > Binder is designed such that a binder_proc never has references to > itself. If this rule is violated, memory corruption can occur when a > process sends a transaction to itself; see e.g. > <https://syzkaller.appspot.com/bug?extid=09e05aba06723a94d43d>. > > There is a remaining edgecase through which such a transaction-to-self > can still occur from the context of a task with BINDER_SET_CONTEXT_MGR > access: > > - task A opens /dev/binder twice, creating binder_proc instances P1 > and P2 > - P1 becomes context manager > - P2 calls ACQUIRE on the magic handle 0, allocating index 0 in its > handle table > - P1 dies (by closing the /dev/binder fd and waiting a bit) > - P2 becomes context manager > - P2 calls ACQUIRE on the magic handle 0, allocating index 1 in its > handle table > [this triggers a warning: "binder: 1974:1974 tried to acquire > reference to desc 0, got 1 instead"] > - task B opens /dev/binder once, creating binder_proc instance P3 > - P3 calls P2 (via magic handle 0) with (void*)1 as argument (two-way > transaction) > - P2 receives the handle and uses it to call P3 (two-way transaction) > - P3 calls P2 (via magic handle 0) (two-way transaction) > - P2 calls P2 (via handle 1) (two-way transaction) > > And then, if P2 does *NOT* accept the incoming transaction work, but > instead closes the binder fd, we get a crash. > > Solve it by preventing the context manager from using ACQUIRE on ref 0. > There shouldn't be any legitimate reason for the context manager to do > that. > > Additionally, print a warning if someone manages to find another way to > trigger a transaction-to-self bug in the future. > > Cc: stable@xxxxxxxxxxxxxxx > Fixes: 457b9a6f09f0 ("Staging: android: add binder driver") > Signed-off-by: Jann Horn <jannh@xxxxxxxxxx> > Acked-by: Todd Kjos <tkjos@xxxxxxxxxx> > --- > sending again because I forgot to CC LKML the first time... sorry about > the spam. This spits out a bunch of warnings when built, how did it work on your end? drivers/android/binder.c: In function ‘binder_thread_write’: ./include/linux/kern_levels.h:5:18: warning: format ‘%d’ expects a matching ‘int’ argument [-Wformat=] 5 | #define KERN_SOH "\001" /* ASCII Start Of Header */ | ^~~~~~ ./include/linux/printk.h:507:10: note: in definition of macro ‘printk_ratelimited’ 507 | printk(fmt, ##__VA_ARGS__); \ | ^~~ ./include/linux/kern_levels.h:14:19: note: in expansion of macro ‘KERN_SOH’ 14 | #define KERN_INFO KERN_SOH "6" /* informational */ | ^~~~~~~~ ./include/linux/printk.h:527:21: note: in expansion of macro ‘KERN_INFO’ 527 | printk_ratelimited(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__) | ^~~~~~~~~ drivers/android/binder.c:147:4: note: in expansion of macro ‘pr_info_ratelimited’ 147 | pr_info_ratelimited(x); \ | ^~~~~~~~~~~~~~~~~~~ drivers/android/binder.c:3646:7: note: in expansion of macro ‘binder_user_error’ 3646 | binder_user_error("%d:%d context manager tried to acquire desc 0\n"); | ^~~~~~~~~~~~~~~~~ ./include/linux/kern_levels.h:5:18: warning: format ‘%d’ expects a matching ‘int’ argument [-Wformat=] 5 | #define KERN_SOH "\001" /* ASCII Start Of Header */ | ^~~~~~ ./include/linux/printk.h:507:10: note: in definition of macro ‘printk_ratelimited’ 507 | printk(fmt, ##__VA_ARGS__); \ | ^~~ ./include/linux/kern_levels.h:14:19: note: in expansion of macro ‘KERN_SOH’ 14 | #define KERN_INFO KERN_SOH "6" /* informational */ | ^~~~~~~~ ./include/linux/printk.h:527:21: note: in expansion of macro ‘KERN_INFO’ 527 | printk_ratelimited(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__) | ^~~~~~~~~ drivers/android/binder.c:147:4: note: in expansion of macro ‘pr_info_ratelimited’ 147 | pr_info_ratelimited(x); \ | ^~~~~~~~~~~~~~~~~~~ drivers/android/binder.c:3646:7: note: in expansion of macro ‘binder_user_error’ 3646 | binder_user_error("%d:%d context manager tried to acquire desc 0\n"); | ^~~~~~~~~~~~~~~~~ thanks, greg k-h _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
