# git rev-parse -q --verify 7b55851367136b1efd84d98fea81ba57a98304cf^{commit}
# git fetch -q -n -f git://fs.ozlabs.ibm.com/kernel/linus master
# git rev-parse -q --verify 7b55851367136b1efd84d98fea81ba57a98304cf^{commit}
7b55851367136b1efd84d98fea81ba57a98304cf
# git checkout -q -f -B kisskb 7b55851367136b1efd84d98fea81ba57a98304cf
# git clean -qxdf
# < git log -1
# commit 7b55851367136b1efd84d98fea81ba57a98304cf
# Author: David Herrmann <dh.herrmann@gmail.com>
# Date:   Tue Jan 8 13:58:52 2019 +0100
# 
#     fork: record start_time late
#     
#     This changes the fork(2) syscall to record the process start_time after
#     initializing the basic task structure but still before making the new
#     process visible to user-space.
#     
#     Technically, we could record the start_time anytime during fork(2).  But
#     this might lead to scenarios where a start_time is recorded long before
#     a process becomes visible to user-space.  For instance, with
#     userfaultfd(2) and TLS, user-space can delay the execution of fork(2)
#     for an indefinite amount of time (and will, if this causes network
#     access, or similar).
#     
#     By recording the start_time late, it much closer reflects the point in
#     time where the process becomes live and can be observed by other
#     processes.
#     
#     Lastly, this makes it much harder for user-space to predict and control
#     the start_time they get assigned.  Previously, user-space could fork a
#     process and stall it in copy_thread_tls() before its pid is allocated,
#     but after its start_time is recorded.  This can be misused to later-on
#     cycle through PIDs and resume the stalled fork(2) yielding a process
#     that has the same pid and start_time as a process that existed before.
#     This can be used to circumvent security systems that identify processes
#     by their pid+start_time combination.
#     
#     Even though user-space was always aware that start_time recording is
#     flaky (but several projects are known to still rely on start_time-based
#     identification), changing the start_time to be recorded late will help
#     mitigate existing attacks and make it much harder for user-space to
#     control the start_time a process gets assigned.
#     
#     Reported-by: Jann Horn <jannh@google.com>
#     Signed-off-by: Tom Gundersen <teg@jklm.no>
#     Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
#     Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
# < /opt/cross/kisskb/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-gcc --version
# < /opt/cross/kisskb/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-ld --version
# < git log --format=%s --max-count=1 7b55851367136b1efd84d98fea81ba57a98304cf
# < make -s -j 8 ARCH=arm O=/kisskb/build/linus_orion5x_defconfig_arm CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-  orion5x_defconfig
# make -s -j 8 ARCH=arm O=/kisskb/build/linus_orion5x_defconfig_arm CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/arm-unknown-linux-gnueabi/bin/arm-unknown-linux-gnueabi-  
/kisskb/src/kernel/printk/printk.c: In function 'devkmsg_sysctl_set_loglvl':
/kisskb/src/kernel/printk/printk.c:186:16: warning: 'old' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/kernel/rcu/srcutree.c: In function 'init_srcu_struct_fields':
/kisskb/src/kernel/rcu/srcutree.c:133:34: warning: 'levelspread[<U58c0>]' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/kernel/rcu/srcutree.c:100:6: note: 'levelspread[<U58c0>]' was declared here
/kisskb/src/drivers/base/regmap/regmap.c: In function 'regmap_raw_read':
/kisskb/src/drivers/base/regmap/regmap.c:2594:6: warning: 'ret' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/drivers/base/regmap/regmap.c: In function '_regmap_raw_write':
/kisskb/src/drivers/base/regmap/regmap.c:1855:6: warning: 'ret' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/drivers/i2c/i2c-core-base.c: In function 'i2c_generic_scl_recovery':
/kisskb/src/drivers/i2c/i2c-core-base.c:235:5: warning: 'ret' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/fs/proc/inode.c: In function 'proc_reg_open':
/kisskb/src/include/linux/list.h:65:12: warning: 'pdeo' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/fs/proc/inode.c:339:21: note: 'pdeo' was declared here
/kisskb/src/fs/udf/unicode.c: In function 'udf_name_conv_char':
/kisskb/src/fs/udf/unicode.c:132:8: warning: 'c' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/net/ipv4/ip_output.c: In function '__ip_append_data':
/kisskb/src/include/linux/skbuff.h:1338:6: warning: 'extra_uref' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/net/ipv4/ip_output.c:885:14: note: 'extra_uref' was declared here
Completed OK
# rm -rf /kisskb/build/linus_orion5x_defconfig_arm
# Build took: 0:01:21.155617