David Daney wrote:
> > 'strace' of this program shows that the system call that returns with -1/EPERM
> > is a call to SYS_6254 (in n32 ABI) or SYS_5250 (in 64 ABI).
> >
> Can you get strace -- version 4.5.20 or later and build it for the
> corresponding ABI? That should properly decode the relevant syscalls.
Version 4.6, built with "gcc -m64", compared to version 4.5.17:
For the program in ABI 64:
strace 4.5.17 reports
SYS_5250() = -1 EPERM (Operation not permitted)
strace 4.6 reports nothing, it stopped the log after it saw an exit() call:
getsockopt(1099511620912, 0xfffff820 /* SOL_??? */, 1099511625776, 0, 0x5555748ed0) = 0
svr4_syscall() = 5012
exit(1099511623472) = ?
fchownat: Operation not permitted
fchownat: Operation not permitted
fchownat: Operation not permitted
For the program in ABI n32:
strace 4.5.17 reports
SYS_6254() = -1 EPERM (Operation not permitted)
strace 4.6 reports
n32_inotify_add_watch(0xffffffffffffff9c, 0x10000a30, 0xffffffff) = -1 EPERM (Operation not permitted)
n32_inotify_add_watch(0xffffffffffffff9c, 0x10000a30, 0x4f0) = -1 EPERM (Operation not permitted)
n32_inotify_add_watch(0xffffffffffffff9c, 0x10000a30, 0xffffffff) = -1 EPERM (Operation not permitted)
For the program in ABI 32:
strace 4.5.17 reports
fchownat(AT_FDCWD, "foo.c", -1, 1264, 0) = 0
fchownat(AT_FDCWD, "foo.c", 1264, -1, 0) = 0
fchownat(AT_FDCWD, "foo.c", -1, -1, 0) = 0
strace 4.6 reports
o32_fchownat(0xffffffffffffff9c, 0x400b00, 0xffffffffffffffff, 0x4f0, 0) = 0
o32_fchownat(0xffffffffffffff9c, 0x400b00, 0x4f0, 0xffffffffffffffff, 0) = 0
o32_fchownat(0xffffffffffffff9c, 0x400b00, 0xffffffffffffffff, 0xffffffffffffffff, 0) = 0
These traces reveal that
- in ABI 32 (the case that works) the value (uid_t)-1 is being passed
to the kernel as 0xffffffffffffffff,
- in ABI n32 (the case that fails) the value (uid_t)-1 is being passed
to the kernel as 0x00000000ffffffff.
Note that 'uid_t' is 'unsigned int' in userland.
Bruno
--
In memoriam Helmuth Hübener <http://en.wikipedia.org/wiki/Helmuth_Hübener>
