Commit adb03115 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller

net: get rid of an signed integer overflow in ip_idents_reserve()

Jiri Pirko reported an UBSAN warning happening in ip_idents_reserve()

[] UBSAN: Undefined behaviour in ./arch/x86/include/asm/atomic.h:156:11
[] signed integer overflow:
[] -2117905507 + -695755206 cannot be represented in type 'int'

Since we do not have uatomic_add_return() yet, use atomic_cmpxchg()
so that the arithmetics can be done using unsigned int.

Fixes: 04ca6973 ("ip: make IP identifiers less predictable")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarJiri Pirko <jiri@resnulli.us>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent fba12966
...@@ -476,12 +476,18 @@ u32 ip_idents_reserve(u32 hash, int segs) ...@@ -476,12 +476,18 @@ u32 ip_idents_reserve(u32 hash, int segs)
atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ; atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ;
u32 old = ACCESS_ONCE(*p_tstamp); u32 old = ACCESS_ONCE(*p_tstamp);
u32 now = (u32)jiffies; u32 now = (u32)jiffies;
u32 delta = 0; u32 new, delta = 0;
if (old != now && cmpxchg(p_tstamp, old, now) == old) if (old != now && cmpxchg(p_tstamp, old, now) == old)
delta = prandom_u32_max(now - old); delta = prandom_u32_max(now - old);
return atomic_add_return(segs + delta, p_id) - segs; /* Do not use atomic_add_return() as it makes UBSAN unhappy */
do {
old = (u32)atomic_read(p_id);
new = old + delta + segs;
} while (atomic_cmpxchg(p_id, old, new) != old);
return new - segs;
} }
EXPORT_SYMBOL(ip_idents_reserve); EXPORT_SYMBOL(ip_idents_reserve);
......
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