drivers/char/random.c: fix boot id uniqueness race
authorMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Thu, 12 Apr 2012 19:49:12 +0000 (12:49 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 12 Apr 2012 20:12:12 +0000 (13:12 -0700)
commit44e4360fa3384850d65dd36fb4e6e5f2f112709b
treebca5390346511ef308933b9968cdc43ec8569b7f
parentd833049bd20570cbbadeb5228c579f9f3aaa4e03
drivers/char/random.c: fix boot id uniqueness race

/proc/sys/kernel/random/boot_id can be read concurrently by userspace
processes.  If two (or more) user-space processes concurrently read
boot_id when sysctl_bootid is not yet assigned, a race can occur making
boot_id differ between the reads.  Because the whole point of the boot id
is to be unique across a kernel execution, fix this by protecting this
operation with a spinlock.

Given that this operation is not frequently used, hitting the spinlock
on each call should not be an issue.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Greg Kroah-Hartman <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
drivers/char/random.c